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A  SUB-SURFACE  IRRIGATION  SEWAGE-DISPOSAL  PLANT. 

Sewage.     Frontispiece. 


Practical  Methods  of 
Sewage  Disposal 


FOR    RESIDENCES,    HOTELS 
AND    INSTITUTIONS 


BY 

HENRY   N.   OGDEN 

M.AM.  SOC.  CE. 
Professor  of  Sanitary  Engineering,  Cornell  University 


H.    BURDETT    CLEVELAND 

ASSOC.  M.AM.  SOC.  C.E. 
Principal  Assistant  Engineer,  New  York  State  Department  of  Health 


FIRST   EDITION 
FIRST  THOUSAND 


NEW  YORK 

JOHN  WILEY  &  SONS 
LONDON:    CHAPMAN  &  HALL,  LIMITED 

1912 


Copyright,  1912,  by 
HENRY  N.  OGDEN 

and 

H.  BURDETT  CLEVELAND 


PUBLISHERS  PRINTING  CO.,  419-421  LAFAYETTE  ST  ,  NEW  YORK 


CONTENTS 

CHAPTER  I.     INTRODUCTORY 

PAGES 

The  problem  of  sewage  disposal.  Composition  and  character  of 
sewage.  Action  of  bacteria.  Soils  and  their  value  for  sewage 
treatment.  Three  essential  conditions  for  effective  sewage  puri- 
fication. Rates  of  operation.  Preliminary  and  final  treatment  I~I3 

CHAPTER  II.    THE  SETTLING  TANK 

Function  and  capacity  of  settling  tanks.  Their  construction. 
Siphon  chambers.  Use  of  concrete.  Pipe  connections.  Roof. 
Baffle  boards.  Imhoff  or  Emscher  tanks 14-36 

CHAPTER  III.    VALVES,  SIPHONS,  AND  SIPHON  CHAMBERS 

Hand  valves.  Gate  valves.  Flap  valves.  _  Various  types  of  siphons. 
Alternating  and  plural  siphons.  Air-lock  siphons.  Dosing 
apparatus • 37~54 

CHAPTER  IV.    SUB-SURFACE  IRRIGATION 

Advantages  of  sub-surface  irrigation  for  sewage  disposal.  Details  of 
system.  Tables  for  use  in  constructing.  Siphon  chambers. 
Sub-surface  tile.  Alternate  use  of  separate  portions  of  area. 
Underdrainage 55~72 

CHAPTER  V.    SEWAGE  FILTERS 

Relative  efficiency  of  various  types.  Sand  Filters.  Tables  for  use  in 
constructing  siphons.  Dosing  and  distribution  methods.  Main- 
tenance. Contact  Beds.  Methods  of  construction.  Alternate 
and  timed  siphons  for  filling  and  discharging.  Table  for  use 
in  constructing.  Sprinkling  Filters.  Their  construction  and 
operation.  Complicated  and  undesirable  for  small  installation  73~97 

CHAPTER  VI.     BROAD  IRRIGATION 

Fertilizing  elements  in  sewage.  Value  of  sewage  for  irrigation. 
Area  required  for  sewage  irrigation.  Methods  of  applying  the 
sewage.  Maintenance  of  irrigated  areas 98-111 

CHAPTER  VII.    ESTIMATES  OF  COST 

Cost  of  material;  of  laying  sewers  and  drains;  of  sand;  of  excavating 
and  refilling;  of  rock  excavation;  of  concrete  work;  of  valves; 
of  dosing  devices;  of  filling  material  for  beds;  of  finishing  and 
cleaning  up.  Table  to  show  items  to  be  considered  in  estimate 
of  cost 1 12-128 

iii 


263612 


LIST   OF   FIGURES 

A  syb-surface  irrigation  sewage-disposal  plant Frontispiece 

FIGURE  PAGE 

1.  Plan  of  settling  tank 15 

2.  Longitudinal  section  of  settling  tank 17 

3.  Sketch  of  settling  tank  with  longitudinal  partition  wall 19 

4.  Forms  used  for  building  side  walls  for  concrete  tank 23 

5.  View  of  settling  tank,  showing  baffles,  sludge  pipe,  drain  pipe,  and 

inlet  and  outlet  pipes 26 

6.  Section  showing  tank  with  concrete  roof  and  form  for  constructing 

roof 28 

7.  Form  for  manhole  opening 30 

8.  Plan  and  longitudinal  section  of  modified  Imhoff  tank 33 

9.  Vertical  cross-section  of  modified  Imhoff  tank 34 

10.  Sludge  valve  for  floor  of  tank 38 

11.  Sludge  valve  for  side  wall  of  tank 39 

12.  Sluice  gate  valve  made  by  Coffin  Valve  Co 40 

13.  Ordinary  gate  valve 40 

14.  English  slide  valve  with  wedge-lock  handle 41 

15.  Flap  valve  attached  to  length  of  sewer  pipe 42 

16.  Flap  valve  with  metallic  seat  attached 43 

17.  Flap  valve  with  loose-link  hinges 44 

18.  Intermittent  dosing  apparatus  made  by  Ansonia  Manufacturing  Co.  45 

19.  Simplest  form  of  automatic  siphon 46 

20.  Van  Vranken  automatic  siphon 47 

21.  Miller  automatic  siphon 48 

22.  Double  alternating  siphons  of  the  Miller  type 49 

23.  Triple  alternating  siphons  of  the  Miller  type 50 

24.  Single  "  Merritt "  automatic  siphon 51 

25.  Air-lock  siphon  for  admitting  and  releasing  sewage  from  each  one  of 

four  beds  in  regular  order 52 

26.  Plan  and  section  of  sub-surface  irrigation  system 61 

27.  Plan  and  section  of  a  portion  of  a  sub-surface  irrigation  system.  ...  62 

28.  Y-branch  of  vitrified  tile  pipe 64 

29.  Eighth  bend  of  vitrified  tile  pipe 64 

30.  Sub-surface  tiling 65 

31.  Photograph  of  tile  laid  as  if  for  sewage  disposal 66 

32.  Sub-surface  tiling  with  broken  stone  or  gravel  surrounding  pipe.  . .  67 

33.  Sub-surface  systems  on  irregular  ground 68 

34.  Special  casting  of  double  Y-branch  with  swinging  gate 69 


VI  LIST   OF   FIGURES 

FIGURE  PAGE 

35.  Double  Y-branch  with  valves  on  branches  of  main  carrier 70 

36.  Sub-surface  tiling  system  with  underdrains 71 

37.  View  of  sand-filter  beds  for  village  in  Massachusetts 75 

38.  Layout  for  intermittent  sand  filtration 78 

39.  Intermittent  sand-filtration  beds 79 

40.  Portion  of  distributing  troughs  for  sand  filters 80 

41.  General  view  of  disposal  plant  at  Bedford  Reformatory 81 

42.  View  of  sand  filter  with  distribution  trough.    Settling  tank  is  at  the 

end  of  the  bed 82 

43.  View  of  diverting  manhole 83 

44.  Plan  of  diverting  manhole 84 

45.  Five-way  diverting  manhole 85 

46.  General  plans  of  contact-bed  system  near  Albany,  N.  Y.,  opposite 

page 89 

47.  View  of  sprinkling  filter  at  Dansville,  Pa.,  in  winter 95 

48.  Distribution  of  sewage  and  arrangement  of  check  levees  on  a  hill- 

side   106 

49.  Distribution  of  sewage  on  a  hillside  of  moderate  slope 107 

50.  Square  beds  for  orchards  according  to  some  Western  practice 108 

51.  Grain- field  in  spring  in  process  of  irrigation 109 


PRACTICAL   METHODS    OF 

SEWAGE    DISPOSAL 

FOR 

RESIDENCES,  HOTELS  AND  INSTITUTIONS 


CHAPTER   I 
INTRODUCTORY 

THE  problem  of  sewage  disposal  for  a  single  house  differs 
from  the  corresponding  problem  for  a  city  chiefly  in  two  ways: 
first,  because  in  the  city  it  is  becoming,  if  it  has  not,  indeed, 
already  become,  a  necessity,  and  city  authorities,  though  some- 
what reluctantly,  are  willing  to  grant  the  necessary  appropria- 
tion to  secure  engineering  advice  which  will  solve  the  problem 
in  a  scientific  as  well  as  economic  fashion.  In  the  case  of  a 
single  house,  whether  a  farm-house  or  a  villa,  the  necessity  of 
employing  competent  engineering  advice  has  not  been  generally 
recognized,  and  no  attempt  has  been  made  to  solve  the  problem 
of  sewage  disposal  in  a  scientific  manner. 

Cesspools  have  been  considered  the  only  way  of  caring  for 
sewage  in  places  where  a  running  stream  was  not  available,  or 
where  attempts  were  made  to  protect  such  a  stream  from 
pollution,  and  while,  in  these  last  few  years,  crude  attempts  have 
been  made  to  utilize  the  so-called  septic  tank,  such  attempts 
have  generally  been  so  unintelligent  that  the  results  have  been 
anything  but  satisfactory.  Since  it  has  been  understood  that 
insects,  such  as  flies  and  mosquitoes,  play  an  important  part 
i  1 


2  PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

in  the  transmission  of  disease,  the  danger  of  overflowing  cesspools 
and  of  open  ditches  in  which  stagnant  sewage  is  present,  has 
been  appreciated;  also  the  higher  standards  of  living  which  have 
made  themselves  felt  throughout  the  rural  community  have 
demanded  in  farm-houses  and  country  homes  sanitary  con- 
veniences which  have  hitherto  been  wanting. 

Gradually  every  house  is  using  more  and  more  water  for 
various  purposes,  and  living  conditions,  which  in  the  past  toler- 
ated a  scanty  supply  drawn  from  a  pump,  are  no  longer  endured. 
The  increased  water  supply  and  the  demands  of  extended 
plumbing  mean  a  greater  amount  of  sewage — so  great  an  amount 
that,  in  many  cases,  soils  which  could  receive  and  digest  the 
waste  waters  from  houses  supplied  by  wells  are  clogged  and 
made  impervious  by  this  greater  amount. 

Further,  the  danger  to  wells  from  the  infiltration  of  cesspools 
is  more  feared,  and  it  is  understood  as  never  before  that  in  order 
to  maintain  the  highest  degree  of  health  in  a  family  the  drinking- 
water  used  must  be  above  suspicion  and  not  subject  to  con- 
taminating influences  in  the  vicinity. 

Again,  communities  are  being  aroused  to  the  intrinsic  value 
of  maintaining  streams  in  a  pure  condition — partly  because  of 
the  value  of  fish  and  ice  coming  from  the  streams  themselves, 
and  partly  on  the  broad  ground  that  watercourses  belong  to  the 
country  as  a  whole,  and  must  be  kept  pure  for  the  sake  of  succeed- 
ing generations,  not  spoiled  for  them  on  account  of  the  selfish- 
ness of  a  few  at  the  present  time. 

Thus  it  is  that  to-day  the  problem  of  sewage  disposal,  while 
arousing  general  interest,  is  recognized  as  one  which  requires 
more  than  the  common  sense  of  an  average  person,  that  the 
force  and  principles  involved  are  understood  to  be  not  those 
in  common  use,  and  that,  for  successful  disposal  of  sewage, 
special  knowledge  and  judgment  are  required. 


INTRODUCTORY  3 

Whatever  the  character  of  the  sewage  and  whatever  the  kind 
of  soil  available  for  treatment,  the  method  of  dealing  with 
sewage  most  obvious  to  most  people  has  been  to  discharge  the 
sewage  directly  into  the  nearest  watercourse.  This  has  been 
the  practice  of  cities  as  well  as  of  individual  houses  in  the  past, 
and  the  practice  is  very  difficult  to  check  because  of  the  econ- 
omy of  this  method  of  disposal.  In  many  cases  there  is  no  objec- 
tion to  this  method,  and  where  a  large  stream  is  available, 
where  no  use  is  made  further  downstream  of  the  waters  for 
drinking  purposes,  and  where  the  volume  of  water  in  the  stream 
is  sufficient  to  dilute  the  sewage  to  a  point  where  no  odors  or 
objectionable  appearances  result,  it  would  seem  most  uneco- 
nomical to  adopt  any  more  complicated  method  of  disposal  than 
by  simply  carrying  the  outfall  pipe  into  the  main  bed  of  the 
stream. 

In  New  York  State,  and  in  a  number  of 'Other  States,  the 
number  of  which  is  continually  increasing,  such  direct  discharge, 
however,  is  not  permitted  by  law  except  under  certain  conditions. 
In  New  York  State  it  is  required  that  any  house,  butter  or 
cheese  factory,  manufacturing  establishment,  or  village  shall 
obtain  the  permission  of  the  State  Commissioner  of  Health 
before  such  a  method  of  discharge  be  adopted,  and  in  order  to 
obtain  this  permission  it  must  be  definitely  shown  that  the 
conditions  of  the  stream  are  such  that  no  reasonable  objection 
to  this  method  could  be  urged.  The  policy  of  the  various  Depart- 
ments of  Health  in  the  United  States  is  gradually  becoming 
more  and  more  rigorous  in  the  matter  of  prohibiting  the  dis- 
charge of  crude  sewage  into  watercourses,  and  it  is  wise  to  make 
very  sure  that  the  discharge  of  sewage  into  streams  is  above  the 
suspicion  of  a  nuisance  before  adopting  this  as  a  suitable  method. 
Rather  would  it  seem  better  to  provide  for  some  method  of  treat- 
ment and  allow  only  purified  sewage  to  go  into  the  stream 


4  PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

than  to  run  the  risk  of  being  forced  in  a  few  years  to  recon- 
struct the  entire  line  of  outfall  pipe,  with  perhaps  an  entire 
reconstruction  of  the  plumbing  within  the  house. 

The  problem  of  treatment  is  the  question  of  so  modifying 
the  character  of  a  large  volume  of  dirty  water  that  it  shall  neither 
injure  the  quality  of  any  drinking-water  into  which  it  may  be 
discharged,  nor  cause  objectionable  odors,  nor  present  dis- 
agreeable appearances  in  any  body  of  water  into  which  it  may 
be  emptied. 

In  order  to  properly  understand  a  reasonable  method  of 
treatment  some  consideration  must  be  given  to  the  composi- 
tion of  sewage.  This  is  chiefly  water  with  which  is  mixed  a  small 
amount  of  animal,  vegetable,  and  mineral  matter.  Roughly 
speaking,  the  amount  of  mineral  dirt  is  about  one  tablespoonful 
to  a  barrelful  of  water,  and  the  combined  amount  of  animal  and 
vegetable  matter  amounts  to  another  tablespoonful.  It  seems 
almost  impossible  that  so  small  a  quantity  of  organic  matter 
as  one  tablespoonful  in  a  barrel  of  water  could  cause  offense 
in  any  way,  and  yet  engineers,  city  officials,  and  householders 
know  by  bitter  experience  that,  when  spread  out  on  the  surface 
of  the  ground  or  when  allowed  to  stand  in  pools,  water  so  pol- 
luted will  undergo  putrefaction  resulting  in  most  disagreeable 
odors  and  in  complete  stagnation.  The  problem  of  sewage 
treatment,  then,  consists  in  removing  from  the  barrelful  of  water, 
the  tablespoonful  of  organic  dirt,  whether  animal  or  vegetable, 
in  such  a  way  that  no  odors  shall  be  occasioned  by  the  process 
and  at  the  same  time  so  that  the  cost  of  the  process  may  be  a 
reasonable  one. 

Unfortunately,  the  greater  part  of  this  organic  matter  is  in 
solution,  dissolved,  like  salt  in  water,  so  that,  though  undeniably 
present,  it  must  be  removed  by  some  process  more  complicated 
and  less  obvious  than  that  of  simple  straining.  It  would  be 


INTRODUCTORY  5 

comparatively  simple  if  the  polluting  substances  remained 
floating  or  suspended  in  the  water.  Then  they  could  be  strained 
out  through  a  fine  sieve  or  settled  out  in  a  tank,  either  with 
or  without  the  aid  of  chemicals.  But  for  particles  in  solution, 
straining,  by  itself,  is  useless  and,  while  in  large  plants  frequent 
use  is  made  of  sieves  as  a  complement  to  the  main  process  of 
purification,  in  small  plants  it  is  of  so  little  value  as  hardly 
to  deserve  consideration. 

Another  factor  enters  to  lessen  the  value  of  the  use  of  screens 
or  sieves  in  an  installation  for  a  single  house.  A  great  deal 
of  the  organic  matter  found  in  sewers  requires  both  agitation  and 
time  for  its  subdivision  into  particles  small  enough  to  be  acted 
upon  in  any  process  of  purification  adopted.  If  a  screen  is  used, 
large  particles  of  putrescible  matter  are  held  on  the  screen 
since  not  enough  time  has  existed  to  break  down  their  mass, 
and  thus  the  screen  itself  becomes  a  most  emphatic  disturbance 
and  a  most  objectionable  feature  of  the  purification  plant. 

For  efficient  purification,  therefore,  some  method  of  reducing 
and  modifying  the  character  of  organic  solids,  particularly  those 
in  solution,  must  be  selected.  In  seeking  a  method  by  which 
this  may  be  accomplished,  scientific  men  found  years  ago  that 
this  very  process  was  being  carried  on  continually  by  natural 
forces,  although  at  a  very  slow  rate  of  purification.  All  organic 
matter,  however  formed  and  wherever  present,  is  subject  to 
the  natural  forces  of  decay.  Fruits,  vegetables,  and  meats 
of  all  kinds,  exposed  to  the  air,  rapidly  lose  their  original  char- 
acter and  form  and  in  the  course  of  time  disappear  entirely. 
Except  for  this  provision  of  nature,  the  accumulation  of  organic 
wastes  since  the  beginning  of  the  earth's  occupation  by  human 
beings  would  be  so  great  that  the  earth  would  be  uninhabitable 
on  account  of  the  deposits  of  waste  matter  which  would  have 
formed  by  this  time.  Nature,  then,  recognizes  the  need  of  dis- 


6  PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

posing  of  organic  wastes,  and  her  method  is  the  one  which 
apparently  must  be  followed  by  human  beings  if  successful 
treatment  is  to  be  secured. 

Only  a  few  decades  ago,  it  was  found  that  this  process  of 
decay  was  due  to  the  activity  of  very  small  organisms  known  as 
bacteria,  and  their  agency  was  proved  by  experiments  which 
showed  that  if  vegetables  or  meat  were  kept  free  from  bacteria, 
no  decay,  fermentation,  or  putrefaction  took  place.  It  was 
proved  that  the  air  itself  was  not  responsible  because  in  certain 
experiments  air  was  allowed  to  enter  through  a  filtering  medium 
fine  enough  to  strain  out  the  bacteria  and  no  decay  took  place, 
although  oxygen  and  air  were  both  freely  admitted.  It  is  well 
understood  by  the  housewife  that  fruits  can  be  kept  indefinitely 
if  they  are  cooked  sufficiently  to  kill  any  bacteria  present  and 
then  sealed  in  bacteria-free,  air-tight  jars.  When  such  preserves 
spoil,  it  is  because  some  bacteria  were  left  in  the  jar  or  have 
since  been  admitted  through  an  imperfect  top.  When  decay  is 
allowed  to  proceed,  the  obvious  result  is,  first  of  all,  a  softening 
of  the  material,  as  in  the  case  of  a  rotten  apple,  a  liquefaction, 
as  it  is  more  technically  known.  Following  that  part  of  the 
process  is  a  gradual  breaking  down  of  the  material,  the  residue 
being  of  an  earthy  character  which  is  assimilated  by  the  soil 
into  which  it  falls. 

The  bacteria  required  for  the  putrefaction  of  organic  matter 
are  among  the  most  widely  distributed  of  all  the  micro-organisms. 
They  are  always  found  in  the  air,  except  on  mountain  tops, 
in  deserts,  and  over  the  ocean.  They  are  very  numerous  in 
surface  waters,  such  as  streams  and  ponds,  and  their  relative 
number  everywhere  increases  as  the  amount  of  organic  matter 
increases,  so  that  the  greater  the  need  for  them  the  greater 
is  their  number.  It  has  been  found  that  the  great  majority 
of  these  bacteria  require  air  for  their  energetic  development, 


INTRODUCTORY  7 

and  this  fact  is  most  important  when  it  comes  to  the  practical 
construction  of  a  piece  of  apparatus  for  making  use  of  these 
bacteria.  It  has  also  been  found  that,  for  several  reasons, 
these  bacteria  work  most  effectively  in  the  soil  and  can  take  care 
of  a  larger  quantity  of  organic  matter  there  than  elsewhere.  This 
is  partly  because  in  the  surface  layers  of  the  soil,  particularly 
where  that  soil  has  been  cultivated,  a  great  number  of  the 
particular  bacteria  involved  in  decay  are  always  to  be  found. 
Pure,  clean  sand  from  the  desert  contains  almost  none  of  these 
beneficent  bacteria.  Rich  garden  soil  is  fairly  teeming  with 
them,  so  that,  curiously,  the  more  organic  matter  and  the  more 
bacteria  present  in  any  soil,  the  more  active  that  soil  will  be  in 
taking  care  of  other  organic  matter. 

Then,  again,  the  soil  particles,  particularly  in  sandy  soil, 
are  so  separated  as  to  allow  between  them  a  certain  and  appre- 
ciable amount  of  air,  and  by  means  of  this  air  the  activity  of 
the  bacteria  is  made  continuous  and  the  products  of  their  activity 
utilized.  Without  such  an  admission  of  air,  the  bacteria  are 
choked  and  diminish  rapidly  in  numbers.  There  is,  however,  a 
definite  degree  of  purification  and  a  certain  quantity  of  organic 
matter  which  can  be  taken  care  of  by  the  bacteria  incident  to  any 
particular  soil.  Up  to  that  quantity  purification  proceeds 
more  or  less  satisfactorily  according  to  the  intelligence  shown  in 
feeding  the  bacteria  in  such  a  way  as  suits  their  convenience. 
If,  however,  that  quantity  be  exceeded,  all  purification  stops, 
the  bacteria  are  apparently  discouraged,  and  no  further  improve- 
ments can  be  expected.  A  fine-grained  soil  will  not  be  so  useful 
as  a  coarse-grained  soil  because  the  former  does  not  allow 
sufficient  air  in  the  interstices  of  its  soil  particles.  Another 
practical  reason  for  not  making  use  of  soils  of  fine  grains  is  that 
such  soils  can  absorb  only  a  small  amount  of  liquid  because 
of  the  mechanical  construction  of  the  material.  On  the  other 


8  PRACTICAL   METHODS   OF    SEWAGE   DISPOSAL 

hand,  soils  whose  grains  are  too  coarse  are  undesirable  because 
their  mechanical  construction  is  such  that  the  liquids  containing 
organic  matter  in  solution  pass  through  so  rapidly  that  time 
enough  is  not  given  for  bacterial  action. 

As  a  result  of  the  principles  just  enumerated,  it  may  be 
said  that  there  are  three  distinct  and  essential  conditions  for 
the  successful  disposal  of  sewage  through  the  soil.  These  three 
conditions  are,  first,  a  rate  of  application  suitable  to  the  soil 
which  it  is  proposed  to  use;  second,  an  interrupted  or  inter- 
mittent delivery  of  the  sewage  so  that  the  bacteria  can  obtain, 
between  consecutive  doses  of  sewage,  the  necessary  amount  of 
oxygen  for  their  own  preservation  and  well-being;  and,  third, 
a  resting  period  in  which  is  carried  forward  that  intimate  associa- 
tion between  the  partly  decomposed  organic  matter  and  the 
oxygen  or  air  present  in  the  pores  of  the  soil  by  which  the  final 
oxidation  is  obtained. 

The  rate  of  application  varies,  as  already  indicated,  with  the 
size  of  particles  found  in  the  soil,  and  it  should  also  vary  with 
the  purification  desired.  The  larger  the  particles,  the  higher  may 
be  the  rate  of  application,  but  less  efficient  will  be  the  process. 
With  grains  of  sand  as  fine  as  1/200  of  an  inch,  and  with  a  rate 
of  application  not  greater  than  five  gallons  per  square  yard  of 
surface  per  day,  filtration  through  such  an  area  has  been  proved 
to  be  capable  of  removing  from  the  foulest  sewage  all  the  objec- 
tionable material  and  converting  the  liquid  into  what  is  an 
equivalent  of  the  purest  spring  water.  If  the  rate  appropriate 
to  this  particular  soil  is  exceeded,  the  efficiency  decreases,  and 
the  unmistakable  and  inevitable  result  is  to  stop  all  purification 
and  convert  the  filter  into  a  stagnant  cesspool.  If,  to  take  the 
other  extreme,  the  soil  particles  are  increased  until  they  are 
as  large  as  hen's  eggs,  then,  if  the  rate  of  application  is  not 
greater  than  200  gallons  per  square  yard  of  surface  per  day, 


INTRODUCTORY  9 

and  if  the  method  and  rate  of  application  are  suitable  to  this 
large  amount,  the  resulting  effluent  is  sufficiently  freed  from  its 
objectionable  matter  so  that  the  liquid  can  be  turned  into  any 
body  of  water  without  danger  of  odors  or  other  nuisance.  If 
this  rate  is  exceeded,  or  if  the  method  of  application  is  not 
carefully  considered,  the  resulting  effluent  is  foul  in  the  extreme 
and  the  process  itself  becomes  a  nuisance. 

It  can  be  seen  by  this  brief  explanation  that  it  is  not  possible 
to  assign  any  particular  rate  of  application  to  any  particular 
kind  of  treatment,  since  in  all  the  methods  of  purification  which 
have  been  worked  out  considerable  variation  in  the  details  of 
that  particular  method  have  been  practised.  It  will  be  possible, 
therefore,  in  succeeding  chapters  to  indicate  by  the  size  of  filters 
recommended  only  limiting  or  average  values  for  rates  of 
purification,  since  those  rates  are  always  dependent  upon  other 
factors  than  the  particular  method  being  discussed.  It  must 
also  be  remembered  that  soils  may  exist  which  have  no  porosity 
whatever,  and  through  which  it  is  impossible  for  sewage  to  make 
its  way.  Such  soils  are  not  available  for  sewage  purification, 
and,  no  matter  how  small  the  rate  or  how  careful  the  method 
of  application,  such  areas  will  fail  to  produce  any  practical 
purification.  Soils  like  clay,  peat,  and  fine  water-deposited  silt 
are  of  this  sort.  Clay  soils  may  sometimes  become  pulverized 
by  cultivation  so  that  they  will  ultimately  be  able  to  take 
care  of  a  moderate  amount  of  sewage.  In  such  a  case  it  is  possible 
to  dispose  of  sewage  successfully  in  the  top  six  inches  of  soil 
which,  by  continual  cultivation,  has  been  made  out  of  the  stiff 
clay.  In  such  cases,  the  difficulty  is  not  that  of  oxidizing  the 
sewage,  but  that  of  taking  care  of  the  effluent,  which  must  be 
held  between  the  cultivated  soil  and  the  raw  clay  underneath. 

The  second  requirement  mentioned  is  secured  by  discharging 
the  sewage  onto  the  soil  area  at  intervals,  the  number  of  doses 


10         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

per  day  depending  upon  the  size  of  particles  in  the  bed.  There 
has  been  a  general  principle  established  that  the  size  of  these 
doses  ought  to  be  smaller  as  the  size  of  the  particles  increases, 
so  that,  whereas  in  the  case  of  sand  beds  the  total  daily  dose 
is  usually  divided  into  from  one  to  three  parts  and  each  part 
delivered  onto  the  bed  with  an  appropriate  interval,  in  the 
case  of  coarser  materials'  used  for  sprinkling  filters,  the  time 
interval  between  doses  is  much  reduced  and  in  some  installations 
recently  constructed  in  England  that  interval  has  been  measured 
in  seconds.  The  variations  in  the  rate  of  flow  of  sewage  onto 
any  filter,  however,  are  so  great  that  any  such  requirement  as 
designing  discharging  apparatus  to  work  at  intervals  of  a  few 
seconds  is  useless,  and  if  as  small  an  interval  as  one  minute  is 
provided  for  the  coarsest  material  for  the  maximum  rate  of  flow 
at  any  time  of  the  day,  the  installation  will  probably  be  suc- 
cessful for  the  lesser  rates  occurring  at  other  times  of  the  day. 
As  an  indication  of  the  way  in  which  this  modification  is  made, 
it  is  customary,  when  the  size  of  soil  particles  is  that  of  peas, 
to  make  the  interval  between  successive  discharges  about  one 
hour,  so  that  the  dose  applied  at  any  one  time  would  be  equal  to 
1/24  of  the  daily  volume.  With  gravel  filling,  the  particles  being 
the  size  of  English  walnuts,  the  interval  between  doses  is  short- 
ened to  five  minutes,  and  the  amount  of  any  one  dose  is  thus  made 
about  1/280  of  the  total  daily  volume.  With  the  coarser  filling, 
as  when  a  size  as  large  as  hen's  eggs  is  used,  the  interval  would 
be  cut  down  to  about  one  minute.  It  should  be  added  that  the 
intervals  last  mentioned  are  characteristic  only  of  some  devices 
used  for  dosing  sprinkling  filters  and  that  there  is  a  wide  diver- 
gence of  practice  among  engineers  when  dealing  with  any  par- 
ticular size  of  sand  or  stone  particles  in  all  kinds  of  filter  beds. 

The  third  requirement,  namely,  the  occasional  resting  of 
the  bed,  is  met  by  providing  some  additional  area  over  that 


INTRODUCTORY  11 

theoretically  required,  so  that  the  flow  may  be  diverted  from  part 
to  part  of  the  total  area  (which  is  usually  divided  into  beds  for 
this  purpose),  and  in  this  way  each  part  is  allowed,  in  turn,  a 
period  for  resting.  For  example,  if  the  required  area  be  divided 
into  two  beds  and  a  third  bed  added  equal  in  area  to  one  of  the 
two  and  a  regular  rotation  of  dosing  be  practised,  each  bed  would 
rest  not  only  the  time  between  the  regular  twelve-hour  period 
dosing,  but  might  also  be  given  a  complete  rest,  occasionally, 
for  an  extended  period.  This  third  requirement  is  probably  less 
imperative  with  the  coarser  particles  and  there  are  many 
examples  of  coarse-grained  beds  which  have  been  continuously 
operated  for  a  period  of  years.  It  is  found,  however,  that  with 
such  treatment  clogging  is  inevitable,  and  that  such  clogging  is 
partially  relieved  by  a  period  of  rest  somewhat  proportional 
to  the  length  of  time  the  beds  have  been  operated.  It  is,  then, 
only  shortsighted  policy  to  economize  at  the  beginning  and 
attempt  to  save  money  by  not  building  an  additional  area, 
since  the  clogging  of  the  whole  plant  is  bound  to  occur  in  the 
course  of  time,  and  then  another  plant  must  be  built  or  the 
material  forming  the  bed  taken  out,  washed,  and  replaced. 
Otherwise  the  sewage  must  go  unpurified  to  the  outfall  while 
the  bed  is  recovering  from  the  long  period  of  overwork. 

It  is  convenient  to  divide  sewage  purification  into  two 
processes,  the  preliminary  process  and  the  final,  or  finishing 
process,  and,  while  the  preliminary  process,  in  itself,  never 
accomplishes  purification,  yet  it  is  of  considerable  value  in  facil- 
itating and  increasing  the  rate  and  efficiency  of  that  purification. 
The  most  common  preliminary  treatment  is  sedimentation,  by 
which  the  larger  solids  in  suspension  are  allowed  to  settle  in 
a  tank  or  tanks  so  that  the  filter  beds  later  used  are  relieved 
from  the  accumulation  of  those  deposits.  Under  the  name  of 
septic  tank  such  a  receptacle  for  suspended  solids  has  been 


12          PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

exploited  as  a  complete  method  of  purification,  and  many 
underground  tanks  have  been  constructed  in  various  parts  of 
the  country  which  have,  at  the  time  of  their  installation,  been 
considered  competent  to  furnish  all  the  necessary  purification. 
When  it  is  remembered  that  less  than  one-half  of  the  organic 
matter  in  sewage  is  in  suspension  and  that  the  best  results  in 
any  sort  of  a  tank  succeed  in  depositing  only  one-half  of  those 
suspended  solids,  it  can  readily  be  seen  that  a  tank,  whether 
called  septic  or  settling,  cannot  be  a  complete  method  of  treat- 
ment. In  reality,  such  a  tank  does  little  more  than  take  out 
from  the  sewage  the  greasy  material  and  a  certain  proportion  of 
the  suspended  matter.  Whatever  part  of  this  is  organic  matter 
may,  by  a  particular  arrangement  of  the  tank,  be  considerably 
reduced  in  quantity,  so  that  the  intervals  of  cleaning  can  be 
extended,  but  in  every  tank  the  removal  of  the  deposits  is 
necessary,  and  subsequent  treatment  is  required  if  adequate 
purification  is  accomplished. 

The  final,  or  finishing,  process  may  be  carried  out  according 
to  any  one  of  several  methods.  It  may  be  done  by  discharging 
the  tank  effluent  into  a  system  of  agricultural  drains  laid  just 
below  the  surface  of  the  ground,  called  sub-surface  irrigation. 
It  may  be  done  by  removing  the  top  soil  from  a  bed  of  sand 
placed  by  nature,  and  needing  little  except  suitable  surface 
distribution  to  insure  the  most  efficient  purification. 

For  a  small  plant,  instead  of  a  sand  filter,  for  which  the 
sand  is  found  naturally  in  a  suitable  location,  an  artificial  filter 
may  be  built  by  preparing  an  enclosure  and  carting  in  sand  for 
filling. 

Where  no  sand  is  available,  or  where  its  use  would  be  uneco- 
nomical, broken  stone  may  be  used  to  ensure  final  treatment. 
With  stone,  on  account  of  its  large  voids,  the  enclosure  must 
either  be  watertight,  and  the  outlet  pipe  must  be  provided  with 


INTRODUCTORY  13 

a  valve  or  other  device  so  that  the  sewage  under  treatment  may 
be  held  in  the  enclosure  or  tank  long  enough  to  deposit  the  solids 
in  suspension  and  to  be  acted  on  by  the  bacteria  concerned. 
This  method  is  known  as  the  contact  bed  treatment.  Or,  fi- 
nally, the  desired  results  may  be  obtained  by  spraying  the  sewage 
onto  a  deep  layer  of  broken  stone,  the  method  being  called 
the  sprinkling  filter  treatment. 

The  choice  of  the  final  treatment,  in  any  particular  case, 
depends  on  the  character  and  slope  of  the  ground,  on  the  avail- 
ability and  cost  of  sand  or  of  broken  stone,  and  on  the  amount 
of  sewage  to  be  treated.  It  is  hoped  that  the  following  pages 
will  give  to  the  reader  both  an  intelligent  appreciation  of  the 
advantages  and  disadvantages  of  each  of  the  several  methods  of 
sewage  purification  discussed,  and  also  sufficient  insight  into  the 
necessary  details  of  construction  so  that  the  method  chosen 
can  be  put  into  successful  operation. 


CHAPTER  II 
THE  SETTLING  TANK  AND  ITS   CONSTRUCTION 

As  has  been  stated,  a  most  effective  preliminary  step  in  the 
treatment  of  sewage  is  to  pass  it  through  a  properly  designed 
settling  tank  in  order  that  the  grosser  solids  and  suspended 
matters  as  far  as  possible  may  be  deposited  there  and  finally 
disposed  of  separately  from  the  liquid  sewage.  This  partial 
removal  of  the  suspended  matters,  amounting  to  about  fifty  per 
cent,  in  well-designed  and  carefully  operated  tanks,  very  mate- 
rially aids  in  the  final  treatment  of  sewage  on  filters  or  on  sub- 
surface irrigation  areas  by  preventing  clogging  of  the  filters  or 
of  the  piping  in  the  irrigation  system. 

In  connection  with  the  larger  settling  tanks  for  hotels  or 
institutions,  it  is  sometimes  advisable  to  pass  the  sewage  first 
through  a  screen  chamber  before  it  is  discharged  into  the 
settling  tank,  in  order  that  the  grosser  suspended  solids  may  be 
collected  more  easily  than  from  the  tank;  but,  as  has  been 
pointed  out,  screening  of  sewage  is  not  necessary  at  small  dis- 
posal plants,  and  in  fact  is  not  generally  advisable  owing  to  the 
continual  labor  involved  in  removing  and  disposing  of  the 
screenings,  and  no  description  of  screening  plants  will  therefore 
be  given. 

The  old  method  of  discharging  sewage  and  house  wastes  into 
loose-walled  cesspools  on  all  occasions  and  under  all  sorts  of 
conditions  is  rapidly  changing,  as  is  desirable.  True,  in  certain 
locations,  where  ample  area  is  available,  where  the  soil  is  dry 
and  porous,  and  where  neither  springs  nor  wells  nor  the  soil  near 

dwellings  will  be  contaminated  thereby,  cesspools  may  be  safely 

14 


16         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

used.  In  other  locations  a  small  expenditure  of  time  and  money 
will  provide  the  means  by  which  nature's  processes  of  reduction 
of  the  organic  matter  in  sewage  may  be  carried  on  much  more 
efficiently  and  satisfactorily  than  ever  can  be  the  case  in  a 
cesspool. 

The  scheme  for  properly  disposing  of  sewage  at  any  point 
should  therefore  include  its  sedimentation  in  a  settling  tank  of 
proper  construction  and  ample  capacity,  whether  its  final  treat- 
ment is  to  be  effected  by  sub-surface  irrigation,  intermittent 
sand  filtration,  contact  beds,  or  sprinkling  filters.  Where  the 
sewage  effluent  is  to  be  discharged  into  a  stream  or  body  of  water 
of  comparatively  large  flow  or  volume,  and  where  that  stream  is 
not  subsequently  used  as  a  potable  water  supply,  it  is  sometimes 
permissible  to  subject  the  sewage  to  settling  tank  treatment 
only.  Such  partial  treatment,  however,  should  be  arranged  for 
only  as  a  temporary  measure,  and  the  tank  should  be  so  con- 
structed with  respect  to  the  elevation  of  adjacent  areas  that 
works  for  final  treatment  of  sewage,  when  required,  may  be 
constructed  as  advantageously  as  possible.  Moreover,  in  the 
more  progressive  States,  as  noted  in  Chapter  I,  the  purity  of 
streams  is  being  carefully  safeguarded,  and  the  general  tendency 
of  public  health  officials  is  to  require  more  complete  treatment 
of  sewage  before  its  discharge  into  a  watercourse  than  is  accom- 
plished by  settling  tanks. 

The  settling  tank  for  residences  and  institutions,  as  shown 
in  Fig.  i,  should  have  a  capacity  of  from  five  to  fifteen  cubic 
feet  for  each  person  served  by  the  sewer  in  order  that  proper 
time  of  detention  in  the  tank  may  be  allowed  for  the  sedimenta- 
tion of  the  suspended  matters  in  the  sewage.  The  depth  of  the 
tank  should  be  from  five  to  eight  feet,  and  its  width  should 
generally  be  from  one- third  to  one-half  the  length.  Fig.  2  shows 
a  longitudinal  section  of  the  settling  tank  and  siphon  chamber. 


18 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


The  following  table  gives  the  dimensions  of  tanks  which 
should  be  adopted  to  provide  a  proper  time  of  detention  of 
sewage,  based  on  the  number  of  persons  to  be  served: 

TABLE  I 
DIMENSIONS  FOR  SETTLING  TANKS 


Persons  Served  by  Sewer. 

Mean  Inside 
Width  (Feet). 

Mean  Inside 
Length  (Feet). 

Depth 
(Feet).* 

-i 

c 

8  

•2 

7 

s 

12  

A 

7  S 

s 

1C 

4' 

8 

25 

A 

10 

7S.  . 

A     S 

12 

c 

SO.  . 

6 

12 

s 

75  

6 

IS 

6 

IOO 

7 

17 

6 

125.  . 

8 

17   5 

6 

ISO.  . 

8 

18 

6 

ITS-  . 

8 

20 

6 

2OO 

8 

22 

6 

250  —  2  compartments  in  tank,  each  .  . 
300—2 
350—2 

400  —  2 
450—2                                                                  .  ... 
500—2 

5-5 

i5 

6 
6 
6 

18 
18.5 
19 
19 

22 
24 

6 

7 

8 
8 
8 

*  12  inches  greater  than  depth  of  sewage. 

The  dimensions  of  settling  tanks  given  above  provide  for 
longer  periods  of  detention  in  the  case  of  the  smaller  tanks  than 
in  that  of  the  larger,  an  excess  which  is  necessary  on  account  of 
the  greater  fluctuation  in  the  flow  of  sewage  reaching  the  smaller 
tanks.  The  larger  tanks  may  be  better  and  more  conveniently 
operated  if  they  are  divided  by  a  longitudinal  partition  wall  as 
shown  by  Fig.  3,  and  arranged  for  in  the  table  for  tanks  serving 
250  or  more  persons.  This  provision  is  not  so  necessary  in  the 
case  of  the  smaller  tanks,  especially  if  they  are  to  be  installed 
at  summer  resorts  or  country  homes  occupied  for  only  a  few 


20          PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

months  in  the  summer.  If,  however,  the  tanks  are  to  be  operated 
continuously  they  may  have  two  chambers  for  greater  conve- 
nience in  removing  sludge.  The  flow  through  one  compartment 
may  then  be  stopped  by  closing  a  valve  placed  on  the  inlet 
pipe  to  that  compartment,  or  by  inserting  one  of  the  stop- 
planks  or  sluices  in  a  diverting  chamber,  as  shown  in  Fig.  3,  at 
the  left  of  the  tank  and  inserting  a  ten-inch  board  in  the  groove 
over  the  outlet  weir  wall  of  the  compartment  to  be  cleaned.  The 
entire  flow  of  sewage  is  then  passed  through  the  other  compart- 
ment while  the  first  is  being  cleaned.  This  division  of  the 
tank  into  two  compartments  is  sometimes  desirable  in  the 
case  of  the  smaller  tanks  and  may  easily  be  accomplished.  For 
instance,  instead  of  a  tank  6  feet  by  12  feet,  two  compartments 
may  be  arranged  for,  each  3  feet  6  inches  by  10  feet;  and 
instead  of  a  tank  8  feet  by  20  feet,  two  compartments  may  be 
constructed,  each  5  feet  wide  and  16  feet  long. 

The  settling  tank  should  be  located  as  far  as  conveniently 
possible  from  the  dwelling,  and  especially  from  any  wells  or 
springs,  in  order  that  leakage  of  sewage,  which  may  always  occur, 
will  not  lead  to  the  contamination  of  a  water  supply  or  of  the 
soil  near  the  residence.  It  may  not  be  possible  in  every  case 
to  locate  such  tanks  more  than  fifty  feet  away  from  the  house 
or  from  the  well,  but  the  distance  should  never  be  less  than  this, 
and  when  located  at  this  minimum  distance  from  the  dwelling 
or  from  a  well,  especial  care  should  be  used  to  make  the  tank 
water-tight. 

The  walls  of  the  tank  should  preferably  be  constructed  of 
concrete,  although  they  may  be  built  of  brick  or  wood.  The 
last  material  is  often  the  cheapest,  and  tanks  constructed  of 
lumber  will  last  for  several  years  without  renewal.  The  concrete 
tank,  however,  is  more  easily  made  water-tight,  and  is  a  per- 
manent structure.  The  walls  of  the  tank,  when  the  height  is  less 


THE   SETTLING   TANK   AND   ITS   CONSTRUCTION       21 

than  8  or  10  feet,  should  be  8  inches  thick  at  the  top,  and 
should  have  a  batter  on  the  inside  of  iX  inches  per  foot  of  height. 
If  the  tank  is  to  be  built  with  two  compartments,  the  partition 
wall  should  be  10  or  12  inches  thick  at  the  top  and  should  have 
a  batter  on  both  sides. 

The  tank  should  generally  be  placed  with  its  top  at  the 
level  of  the  ground  surface,  and  the  sewer  from  the  house  should 
enter  the  end  of  the  tank  with  its  flow  line  or  invert  12  inches 
below  the  top  of  the  walls.  The  house  sewer  or  drain  should  have 
a  grade  or  fall  of  not  less  than  9  inches  in  100  feet.  Preferably, 
the  sewer  should  be  laid  at  the  above  minimum  grade  for  at 
least  50  feet  or  so  before  it  enters  the  tank  in  order  to  prevent 
excessive  velocity  in  the  sewage  flow  at  this  point.  At  the 
entrance  to  the  tank  the  sewer  should  be  provided  with  an 
elbow  so  that  the  sewage  will  be  discharged  downward  below  the 
surface.  Similarly,  if  an  outlet  pipe  from  the  tank  is  used,  as 
shown  in  Fig.  5,  this  pipe  should  pass  through  the  wall  at  the 
outlet  end  of  the  tank,  one  foot  below  the  top  of  the  tank,  and 
should  also  be  provided  with  an  elbow  which  will  start  from 
below  the  surface. 

Where  a  siphon  is  to  be  used  to  discharge  the  effluent  from 
the  tank  onto  a  filter  or  into  a  system  of  sub-surface  tiling, 
the  separate  chamber  in  which  the  siphon  must  be  placed  may 
be  built  as  an  extension  of  the  settling  tank  so  that  the  end  wall 
of  the  settling  tank  will  serve  as  one  of  the  walls  of  the  siphon 
chamber. 

The  siphon  chamber  floor  may  be  placed  considerably  above 
the  level  of  the  floor  of  the  tank  as  shown  in  Figs.  2  and  3, 
since  a  sufficiently  large  quantity  of  effluent  for  dosing  a  filter 
or  a  sub-surface  irrigation  system  may  be  collected  in  the 
chamber  of  reduced  depth  thus  provided.  This  shallower  con- 
struction saves  excavation  and  also  reduces  the  operating  head 


22         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

or  fall,  which  latter  is  sometimes  hardly  equal  to  the  demands 
of  the  subsequent  treatment.  The  capacity  needed  in  this 
chamber  for  different  installations  will  be  given  later  in  the 
discussion  of  sewage  niters  and  sub-surface  irrigation  systems. 

Having  determined  upon  the  dimensions  of  the  tank  and 
selected  the  site,  the  construction  is  commenced  by  making 
the  excavation  about  four  feet  wider  and  longer  than  the  outside 
dimensions  of  the  tank  and  siphon  chamber  combined,  in  order 
to  provide  room  for  setting  the  forms  for  placing  the  concrete, 
provided  concrete  is  to  be  used  in  its  construction.  With  brick 
walls  an  additional  width  and  length  of  two  feet  is  needed. 

Fig.  4  gives  an  illustration  of  the  forms  to  be  used  in  con- 
structing the  walls  for  concrete  tanks,  the  cut  at  the  left  showing 
a  view  of  the  form  to  be  used  when  the  tank  is  constructed  either 
partly  or  wholly  above  the  natural  ground  surface,  or  below  the 
surface  in  loose  soils,  and  the  cut  at  the  right  showing  a  view 
of  the  form  to  be  used  when  excavation  for  the  tank  is  made  in 
rock,  hardpan,  or  clay.  The  top  width  of  the  walls  should  be 
8  inches,  and  the  bottom  width  should  be  8  inches  plus  i>£ 
inches  for  each  foot  of  height.  Thus,  for  a  wall  6  feet  high  the 
bottom  width  should  be  17  inches, — the  inside  face  of  the  wall 
having  a  batter  of  i^  inches  per  foot  of  height.  This  batter  is 
necessary,  when  the  tank  is  constructed  below  the  ground  sur- 
face, to  withstand  the  lateral  earth  pressure  when  the  tank  is 
empty.  If  the  tank  is  to  be  constructed  above  the  ground 
surface,  the  outside  wall  should  be  battered  and  the  inside  wall 
made  vertical,  since  the  pressure  which  the  wall  must  with- 
stand is  then  only  from  the  liquid  within  the  tank.  The  parti- 
tion wall  between  the  settling  tank  and  siphon  chamber  should 
be  10  or  12  inches  thick  at  the  top,  depending  on  its  height, 
and  should  have  a  batter  on  both  sides. 

To  set  up  the  forms  for  the  concrete  walls,  stakes  2  inches  by 


THE   SETTLING   TANK   AND    ITS   CONSTRUCTION       23 

4  inches  and  about  1^2  feet  long  are  first  driven  on  each  side 
of  the  bottom  of  the  wall,  and  6  inches  away,  from  the  wall  as 
laid  out,  at  intervals  of  2  feet.  Pieces  of  scantling,  2  inches  by 
4  inches  and  with  a  length  equal  to  the  height  of  the  wall,  are 
then  placed  in  upright  position  and  securely  nailed  to  these 


v-r$£*: 
FIG.  4. — Forms  Used  for  Building  Side  Walls  for  Concrete  Tank. 

stakes.  The  inner  scantling  are  then  inclined  and  temporarily 
fastened  at  the  top  by  a  short  nailing  piece  to  the  outer  row  so 
as  to  leave  an  opening  of  10  inches  between  each  pair  of  scantling. 
Additional  stakes  are  then  driven  from  2  to  4  feet  from  the  wall 
on  each  side,  as  shown  in  the  illustration,  and  braces  2  inches 


24         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

thick  and  3  inches  or  4  inches  wide  are  nailed  to  these  stakes 
and  to  the  upright  and  inclined  scantling.  One-inch  boards 
are  then  lightly  nailed  to  the  scantling,  as  shown,  the  boards 
making  up  the  inside  face  of  the  form  being  placed  in  sections  of 
two  feet  in  order  to  afford  opportunity  for  thorough  tamping  of 
the  concrete  as  the  form  is  being  filled.  The  concrete  is  then 
placed  between  the  boarded  sides  of  the  form  in  6-inch  layers 
and  well  rammed. 

The  concrete  should  be  composed  of  one  part  by  measure 
of  Portland  cement  to  two  and  a  half  parts  of  clean,  sharp 
building  sand  and  five  parts  of  broken  stone  or  clean  gravel. 
The  cement  and  sand  should  first  be  thoroughly  mixed,  while 
dry,  to  an  even  color  and  then  wet  and  tempered  to  a  soft  mortar. 
The  broken  stone  or  gravel,  after  having  first  been  thoroughly 
wet,  should  be  spread  evenly  over  the  batch  of  mortar  and  the 
mass  shoveled  over  at  least  three  times  to  insure  a  thorough 
coating  of  the  stones  with  mortar.  The  concrete  thus  made  may 
then  be  placed  in  the  forms  in  six-inch  depths  and  thoroughly 
rammed  until  water  covers  the  surface. 

When  it  is  essential  that  the  tank  be  water-tight,  and,  in  fact, 
in  constructing  all  tanks,  each  layer  of  concrete  should  be 
placed  between  the  forms,  when  possible,  before  the  concrete 
in  the  layer  previously  placed  has  set.  If  the  work  of  placing  the 
concrete  is  of  necessity  interrupted,  before  placing  another 
layer  the  surface  of  the  older  concrete  should  first  be  sprinkled 
and  swept  with  a  stiff  broom  and  a  thin  coating  of  neat  cement 
mortar  (containing  no  sand)  should  then  be  washed  over  the 
surface  of  the  concrete. 

It  may  be  noted  that  a  barrel  of  Portland  cement  (equal  to 
four  bags)  contains  3.8  cubic  feet,  so  for  concrete  with  the 
proportions  of  cement,  sand,  and  stone  as  specified  above,  for 
each  barrel  of  cement  used  there  should  be  used  9.5  cubic  feet 


THE    SETTLING   TANK   AND   ITS   CONSTRUCTION       25 

of  loose  sand  and  19  cubic  feet  of  loose  stone;  and  for  each 
cubic  yard  of  concrete  required  there  will  be  needed  1.30  barrels 
(or  5.2  bags)  of  cement,  0.46  cubic  yards  of  sand,  and  0.92  cubic 
yards  of  stone  if  the  stone  is  fairly  uniform  in  size  and  contains 
forty-five  per  cent  of  voids.  With  stone  or  gravel  less  uniform  in 
size,  less  cement  and  sand  is  required.  The  cement  and  sand, 
made  into  mortar,  will  fill  the  voids  or  open  spaces  in  the  mass 
of  broken  stone.  (For  further  details  see  Chapter  VII.) 

As  shown  in  the  illustration  (Fig.  4),  the  foot  of  each  upright 
and  inclined  scantling  should  be  placed  at  the  proposed  eleva- 
tion of  the  floor  of  the  tank,  and  the  boarding  should  not  be 
carried  below  this  level.  Then,  if  the  excavation  for  the  wall 
has  been  carried  to  a  level  6  or  8  inches  lower  than  the 
floor  of  the  tank,  the  concrete  when  being  placed  between  the 
forms  will  spread  under  the  bottom  of  the  forms,  making  a  footing 
for  the  wall  on  the  outside  and  better  insuring  a  water-tight 
joint  when  the  floor  is  laid  against  the  inside  foot  of  the  walls. 

In  making  the  excavation  for  the  tank,  after  reaching  the 
proposed  level  for  the  floor  a  trench  should  be  cut  around  the 
floor  space  to  a  depth  of  6  to  8  inches  below  the  floor  level. 
The  width  of  this  trench  should  be  such  as  to  extend  from  6 
to  8  inches  inside  and  an  equal  distance  outside  the  wall  at  the 
floor  level.  After  the  walls  have  been  constructed  as  described, 
the  forms  should  be  left  in  place  for  at  least  24  hours,  to  allow 
the  concrete  to  set,  and  then  removed.  The  excavation  inside 
the  walls  should  then  be  carried  6  inches  below  the  floor  level, 
the  soil  well  tamped,  and  a  6-inch  layer  of  concrete  placed  to 
form  the  floor  of  the  tank.  It  is  well  to  sprinkle  all  concrete 
daily  until  it  has  thoroughly  set. 

If  the  type  of  siphon  selected  has  a  U-shaped  pipe  extending 
below  the  floor  of  the  siphon  chamber,  it  will  be  necessary  to 
set  the  siphon  in  position  while  the  floor  is  being  laid  and  the 


26 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


discharge  pipe  in  position  while  the  wall  is  being  laid.  The 
siphon  should  be  so  placed  that  the  bottom  of  the  bell  over  the 
longer  leg  is  3  inches  above  the  floor  of  the  siphon  chamber 
or  of  the  sump  in  the  siphon  chamber  if  such  a  depression  is  made 
in  the  construction  of  the  floor. 

The  floor  of  the  tank  should  slope  toward  the  inlet  end 
at  a  rate  of  one-half  inch  per  foot  of  length  in  order  to  facilitate 
the  removal  of  sludge  when  the  tank  is  being  cleaned.  This  will 
result  in  providing  a  somewhat  greater  depth  at  the  inlet  end 


FIG.  5.— View  of  Settling  Tank,  Showing  Baffles,  Sludge  Pipe,  Drain  Pipe,  and 
Inlet  and  Outlet  Pipes. 

of  the  tank  than  is  shown  by  the  tables,  and  a  lesser  depth  at 
the  outlet  end,  leaving  the  depth  at  the  centre  of  the  tank  as 
shown.  The  inlet  and  outlet  pipes  to  the  tank,  which  should  be 
of  cast  iron,  should  be  placed  in  position  through  the  forms 
while  the  walls  are  being  laid. 

When  it  is  desired  to  have  an  outlet  pipe  from  the  tank 
near  the  bottom  (see  pipe  A,  Fig.  5),  for  the  purpose  of  drawing 
off  the  supernatant  liquid,  and  so  saving  the  labor  of  removing 
the  liquid  by  pail  when  the  tank  is  being  cleaned,  this  pipe 
should  be  of  cast  iron,  4  inches  in  diameter  and  fitted  with  a  valve 


THE   SETTLING   TANK   AND   ITS   CONSTRUCTION       27 

and  valve  rod  placed  outside  the  tank,  and  should  also  be  placed 
in  position  during  the  construction  of  the  tank.  The  valve  rod, 
or  stem,  should  reach  to  the  surface  of  the  ground  through  a 
3 -inch  pipe  casing.  The  lower  outlet  pipe  should  be  extended 
around  the  siphon  chamber  to  discharge  into  the  effluent  pipe 
leading  away  from  this  chamber,  when  possible.  This  lower 
outlet  pipe  should  leave  the  tank  at  least  one  foot  above  the  floor 
and  sometimes  at  a  higher  elevation,  in  order  to  discharge  into 
the  sewer  leading  to  the  irrigation  field  or  to  the  filter. 

Pipe  B  in  Fig.  5  shows  a  sludge  pipe  which  may  be  laid  to  a 
suitable  site  for  disposing  of  sludge  from  the  tank  when  the 
slope  of  the  land  will  permit  the  draining  of  the  sludge  by 
gravity  into  trenches  or  onto  a  sludge  bed.  This  sludge  pipe 
should  be  fitted  with  a  valve  and  valve  stem,  and  the  valve 
may  be  inside  the  tank,  as  shown  in  the  illustration,  or  outside 
the  tank,  as  shown  on  pipe  A.  If  such  an  arrangement  for  dis- 
posing of  sludge  is  possible,  it  is  manifestly  unnecessary  to  provide 
pipe  A  as  shown  in  Fig.  5,  since  the  supernatant  liquid  as  well 
as  the  sludge  may  then  be  piped  to  a  sludge  bed  or  pit.  This 
bed  should  be  shallow,  but  of  ample  capacity  to  hold  the  entire 
contents  of  the  settling  tank.  The  sludge  may  then  be  drawn 
off  about  every  six  weeks,  thereby  operating  the  tank  as  a 
settling  tank  rather  than  as  a  septic  tank.  It  will  be  found  after 
scum  of  a  certain  thickness  has  formed  on  the  surface  of  the 
sewage  in  the  tank  that  the  thickness  will  not  materially 
increase. 

The  roof  of  the  tank  should  preferably  be  of  concrete  reen- 
forced  with  iron  rods,  although  it  may  be  of  brick  arches  or  of 
two-inch  planking.  The  use  of  brick  for  the  roof  is  not  advisable, 
however,  since  the  forms  for  the  construction  of  the  arches  are 
rather  difficult  to  make,  and  brick  roofs  are  apt  to  be  broken 
down  sooner  or  later  through  the  action  of  frost.  A  wooden 


28 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


roof,  also,  must  be  renewed  at  intervals  and  is  not  as  satis- 
factory as  a  concrete  roof. 

A  section  of  a  tank  with  a  concrete  roof  is  shown  by  Fig.  6, 
together  with  the  temporary  form  built  up  inside  the  tank  on 


FIG.   6. — Section  Showing  Tank  with   Concrete   Roof  and   with   Form  for 
Constructing  Roof. 

which  to  lay  the  roof.  The  form  is  built  by  setting  2-inch  by 
4-inch  scantling  on  wedges  along  the  walls  of  the  tank  in  pairs 
1 8  inches  apart  and  bracing  these  at  the  foot.  Boards  i^ 
inches  thick  and  10  inches  wide  are  then  nailed  across  the  tank 
to  the  tops  of  the  scantling,  the  top  edges  of  the  boards  being 


THE    SETTLING   TANK   AND   ITS    CONSTRUCTION       29 

i  inch  below  the  top  of  the  walls.  A  false  roof  is  then  made 
of  boards  nailed  lengthwise  of  the  tank  to  the  lo-inch  boards, 
and  a  layer  of  concrete  2  inches  thick  is  then  placed  on  the  floor 
thus  made,  reaching  over  the  top  of  the  walls  to  the  outside 
edges.  Iron  rods,  ^  of  an  inch  thick  and  spaced  i  foot  apart, 
are  then  placed  on  the  concrete  across  the  tank  and  reaching 
to  within  i  inch  of  the  outside  edges  of  the  walls.  More  con- 
crete is  then  placed  over  the  first  layer  to  a  total  depth  of  6 
inches  or  8  inches,  depending  on  the  width  of  the  tank,  the 
concrete  being  well  rammed  as  it  is  placed.  After  the  concrete 
has  set,  the  wedges  may  be  knocked  from  under  the  upright 
scantling  and  the  form  taken  down  and  removed  through  the 
manhole.  The  manhole  covers  and  frames,  as  shown  in  the 
illustrations  in  Chapter  III,  may  be  cast  at  local  foundries  or 
purchased  through  sewer-pipe  dealers. 

To  provide  manholes  or  openings  through  the  roof  into  the 
tank  and  into  the  siphon  chamber,  round  openings  2  feet  in 
diameter  should  be  cut  in  the  false  roof  while  it  is  being  laid, 
the  distance  between  the  pairs  of  scantling  at  this  point  being 
made  2  feet.  The  manhole  frames  should  then  be  so  placed 
that  the  flange  or  base  of  the  frame  will  be  imbedded  to  a  depth 
of  2  inches  in  the  roof  when  completed.  The  manhole  at  the 
entrance  end  of  the  tank  should  be  located  at  one  side  of  the 
entrance  pipe  and  over  the  valve  on  the  sludge  pipe.  To  pro- 
vide the  necessary  opening  through  the  concrete  roof  below  the 
manhole  frame,  an  eight- sided  wooden  form,  as  shown  in  Fig.  7, 
with  an  inner  diameter  of  2  feet  and  a  height  equal  to  2%  inches 
less  than  the  thickness  of  the  roof,  is  placed  over  the  opening  in 
the  false  roof.  On  this  wooden  form  the  manhole  frame  is  placed 
and  the  concrete  laid  around  the  form  and  over  the  flanges 
of  the  manhole  frame.  Two  of  the  ^-inch  iron  rods  should  be 
placed  across  the  tank  close  to  each  side  of  the  wooden  form 


30         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

after  the  first  2 -inch  layer  of    the    concrete    roof   has    been 
placed. 

When  it  is  desired  to  carry  the  manhole  some  distance  above 
the  level  of  the  top  of  the  roof  to  provide  for  a  rather  deep 

Square  corners  to  be  -3^.   V*.  Cartn   COVCring   for    the    tank,  the 

sawed  off  when  form^^^^^  .,.,,,  ,  -  , 

is  compieted^^^|^^™[^^j  eight-sided  wooden  form  may  be 

made  deeper  as  desired,  and 
another  larger,  similar  form  built 
for  the  outside  form  of  the 
necessary  concrete  manhole  well. 
The  space  between  the  two  forms 

FIG.  7. — Form  for  Manhole  Opening. 

may  then  be  filled  with  con- 
crete and  the  manhole  frame  set  on  the  octagonal-shaped  wall 
thus  formed. 

In  order  to  insure  a  more  uniform  flow  of  sewage  through 
the  tank  and  thus  reduce  the  velocity  of  flow  in  all  portions 
to  a  minimum,  baffle  boards  of  2 -inch  planks  should  be  placed 
across  the  tank  near  the  inlet  pipe  and  near  the  outlet  pipe,  as 
shown  in  Fig.  5.  These  boards  are  set  in  grooves  formed  in  the 
concrete  by  nailing  i-inch  by  3 -inch  strips  to  the  inside 
form  when  the  tank  wall  is  constructed.  These  baffles  also 
serve  a  useful  purpose  by  reducing  the  disturbance  of  the  scum 
as  the  sewage  enters  the  tank  and  by  preventing  the  escape  of 
scum  from  the  tank. 

The  boards  should  extend  to  a  depth  of  one  foot  below  the 
inlet  and  outlet  pipes,  and  should  usually  be  placed  12  to 
1 8  inches  from  the  ends  of  the  tank.  Where  the  effluent 
from  the  tank  is  to  be  collected  in  a  siphon  chamber  adjoining 
the  tank,  it  is  preferable  to  provide  a  weir  or  wall  between  the 
tank  and  the  siphon  chamber.  The  top  of  this  wall  should  be 
one  foot  below  the  roof  to  allow  the  effluent  to  flow  over  this 
wall  from  the  tank  into  the  siphon  chamber.  In  this  case  no 


•     THE   SETTLING   TANK   AND   ITS  CONSTRUCTION       31 

outlet  pipe  from  the  tank  is  used,  and  the  baffle  boards  should 
extend  downward  12  inches  below  the  level  of  the  sewage  in 
the  tank.  These  baffle  boards  should  be  carried  up  to  a  level 
with  the  top  of  the  tank  walls. 

It  is  advisable  to  provide  an  overflow  pipe  from  the  siphon 
chamber  which  should  leave  this  chamber  at  an  elevation  of 
3  or  4  inches  above  that  of  the  inlet  pipe  to  the  tank, 
and  which  should,  by  means  of  an  elbow,  be  extended  down 
outside  the  chamber  to  connect  with  the  sewer  into  which  the 
siphon  discharges.  This  is  desirable  in  order  to  provide  an 
overflow  in  case  the  siphon  becomes  clogged  or  fails  to  operate. 

Where  a  tank  must  of  necessity  be  located  near  a  residence, 
any  nuisance  due  to  odors  may  be  prevented  by  inserting  a 
4-inch  galvanized-iron  conductor-pipe  through  the  roof  of 
the  tank,  and  carrying  this  pipe  up  into  the  air  20  or  30  feet 
along  a  tree  trunk  or  the  side  of  a  building. 

If  a  sub-surface  irrigation  field  is  to  be  laid  out,  the  tank 
should  preferably  be  near  the  proposed  location  of  the  sub- 
surface irrigation  area  (see  Fig.  26,  Chapter  IV),  although  the 
effluent  may  be  carried  to  the  sub-surface  irrigation  field  from 
a  settling  tank  located  at  some  distance  from  such  field.  Since 
the  sewage  enters  the  tank  near  the  top  of  the  tank  and  the 
effluent  discharges  from  the  siphon  chamber  at  a  considerable 
distance  below  the  top  of  the  tank,  it  is  of  advantage  to  place 
the  settling  tank  on  sloping  ground,  if  possible,  so  that  one  end 
will  be  wholly  in  excavation  and  the  other  will  be  partly  above 
the  natural  ground  surface.  This  reduces  the  depth  of  trenching 
and  provides  for  more  readily  distributing  the  effluent  by  gravity 
from  the  tank  through  the  sub-surface  tiling  which  is  laid  just 
below  the  surface  of  the  ground.  The  tank  must  always  be  higher 
than  the  distributing  field  to  allow  for  the  flow  of  sewage,  and 
it  is  desirable  to  have  the  tank  buried  in  the  ground  if  possible 


32         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

in  order  to  keep  the  temperature  of  the  sewage  as  high  as  possible 
in  winter.  These  ideal  conditions  are  not  always  to  be  attained. 

The  one  important  point  to  be  kept  in  mind  if  the  settling 
tank  is  to  be  properly  operated  and  not  allowed  to  develop  into  a 
nuisance  is  that  the  sludge  or  sediment  must  be  removed  from 
the  bottom  of  the  tank  at  intervals  before  the  effective  capacity 
of  the  tank  is  so  reduced  that  the  proper  sedimentation  of  the 
sewage  is  impossible.  The  frequency  of  cleaning  necessary  varies 
in  different  cases,  but  usually  the  tank  should  be  emptied  and 
cleaned  at  intervals  of  from  three  months  to  one  year,  and  where 
the  contour  of  the  ground  allows  the  sludge  to  be  readily  drawn 
off  into  trenches  or  to  a  sludge  bed,  cleaning  should  be  prac- 
tised every  five  or  six  weeks. 

There  is,  perhaps,  little  need  for  cleaning  the  tank  as  often 
as  once  in  six  weeks,  but  it  is  generally  found  and  has  been 
affirmed  in  court  testimony  that  the  removing  of  the  sludge  from 
a  settling  tank  once  every  six  weeks  will  prevent  septic  action 
from  taking  place,  and  the  tank  will  then  be  operated  as  a 
settling  tank  and  not  as  a  septic  tank.  This  is  desirable  in  view 
of  the  fact  that  royalties  have  been  claimed  under  certain 
patents  on  septic  tanks.  As  explained  on  p.  n,  the  important 
function  of  the  tank  is  to  settle  out  suspended  solids,  while 
the  processes  that  take  place  in  the  septic  tank  but  not  in  the 
settling  tank  are  of  minor  importance,  and  it  is  advisable 
therefore  to  operate  these  tanks  as  settling  tanks  when  possible. 

In  no  case  should  the  sludge  be  allowed  to  accumulate 
until  it  fills  more  than  one-quarter  of  the  tank.  The  sludge 
may  be  disposed  of  by  burying  in  trenches  or  ploughing  under, 
or  it  may  be  spread  on  the  surface  at  points  remote  from  high- 
ways and  dwellings  or  sources  of  water  supply.  The  depth  of 
accumulated  matter  in  the  tank  should  frequently  be  tested  at 
the  inlet  end  by  using  a  pole  or  stick. 


,  — 
Vofl 


>c 


Angle  iron  to 
upport  Baffle  Board 


em 


from  foot  of 

/all  to  Partitio 

(laid  on  angle  iron) 


FIG.  8. — Plan  and  Longitudinal  Section  of  Modified  Imhoff  Tank. 
3 


34 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


In  reference  to  the  preliminary  treatment  of  sewage  in 
tanks,  it  should  be  noted  that  the  most  recent  development  in 
the  design  of  sewage-disposal  plants  has  been  the  improved 
method  of  sedimentation  of  sewage  represented  by  the  Imhoff 
or  Emscher  tank.  A  modified  design  of  this  tank  is  shown  in 
plan  and  longitudinal  section  in  Fig.  8,  and  a  cross-section  of 
the  tank  is  shown  in  Fig.  9.  The  principle  employed  is  to  provide 
a  separate  chamber  for  storing  the  sludge  which  results  from 


FIG.  9. —  Vertical  Cross-Section  of  Modified  Imhoff  Tank. 


the  sedimentation  of  the  suspended  matters  in  the  sewage, 
this  chamber  being  almost  entirely  separated  from  the  portion 
of  the  tank  in  which  the  sedimentation  takes  place.  This 
separation  of  the  sludge  from  the  flowing  sewage  is  accom- 
plished in  the  tank  shown  by  inserting  in  the  tank,  parallel 
with  the  side  walls,  two  inner  partitions  AA,  which  are  vertical 
for  a  few  feet  below  the  surface  of  the  sewage  and  then  slope 
toward  the  centre  line  of  the  tank,  but,  as  shown  by  Fig.  9,  do 


THE    SETTLING    TANK   AND    ITS    CONSTRUCTION       35 

not  meet  at  the  centre  line,  the  one  passing  a  few  inches  under 
the  other.  The  opening  or  slot  thus  formed  between  the  two 
inner  partitions  allows  the  suspended  matters  which  settle  out 
of  the  sewage  flowing  through  the  upper  compartment  to  pass 
into  the  lower  or  sludge  compartment  and  there  remain  in  a 
quiescent  state  until  removed  from  the  tank.  The  object  of  this 
separation  of  the  sludge  from  the  flowing  sewage  is  to  prevent 
the  gas  bubbles  which  emanate  from  the  sludge  during  its 
decomposition  from  rising  through  the  flowing  sewage  and  in- 
terfering with  the  process  of  sedimentation  going  on  in  the  upper 
compartment,  and  to  provide  for  a  more  complete  decom- 
position or  " digestion"  of  the  sludge.  The  gas  bubbles  on  rising 
from  the  deposited  sludge  strike  the  sloping  lower  sections  of 
the  inner  partitions  and  are  deflected  to  the  portions  of  the 
tank  next  to  the  outside  walls.  A  sludge  pipe  leads  away  from 
the  bottom  of  the  hopper-shaped  sludge  compartment,  and  at 
intervals  of  from  one  to  four  weeks  the  valve  on  this  sludge 
pipe  is  opened  for  a  short  time  and  a  small  portion  of  the  accu- 
mulated sludge  is  allowed  to  be  forced  out  onto  a  sludge-drying 
bed  by  the  weight  of  the  sewage  in  the  tank.  The  portion  of 
the  sludge  thus  removed  has,  of  course,  remained  in  the  tank 
the  longest  time,  generally  five  or  six  months,  and  has  had  the 
fullest  opportunity  to  be  reduced  and  rendered  inodorous  and 
easy  to  dispose  of. 

This  method  of  sedimentation  was  first  experimented  with 
about  twelve  years  ago  by  Mr.  H.  W.  Clark  at  the  Lawrence 
Experiment  Station  of  the  Massachusetts  State  Board  of  Health, 
then  partially  developed  by  Dr.  W.  Owen  Travis,  of  Hampton, 
England,  and  finally  worked  out  by  Dr.  Ing.  Carl  Imhoff  in 
connection  with  the  disposal  of  sewage  in  the  Emscher  River 
district  in  Germany.  The  method  has  been  extensively  and 
successfully  used  in  Germany,  and  similar  tanks  are  now  being 


36          PRACTICAL    METHODS    OF    SEWAGE    DISPOSAL 

installed  in  this  country.  While  these  tanks  are  probably  more 
effective  than  septic  tanks  and  the  usual  type  of  settling  tanks 
in  the  removal  of  suspended  matters  in  sewage,  their  chief  value 
will  undoubtedly  be  found  in  the  rendering  of  the  sludge  less 
odorous  and  more  easily  handled.  This  form  of  settling  tank 
is  covered  by  patents,  and  a  moderate  royalty  is  charged  on  tanks 
of  this  type. 

A  description  of  the  Imhoff  tank  has  been  here  included 
since  it  represents  an  important  development  in  sewage  disposal 
and  helps  to  solve  what  has  heretofore  been  one  of  the  main 
difficulties  of  sewage  disposal,  especially  for  cities  and  villages, 
namely,  the  satisfactory  and  convenient  disposition  of  sludge; 
but  it  is  not  considered  that  their  construction  is  advisable  or 
warranted  where  only  a  small  quantity  of  sewage  is  to  be  treated, 
and  settling  tanks  to  treat  sewage  contributed  by  less  than,  say, 
two  hundred  persons  would  generally  be  constructed  as  pre- 
viously described. 


CHAPTER   III 
VALVES,  SIPHONS,  AND    SIPHON   CHAMBERS 

It  was  explained  in 'Chapter  I  that  one  of  the  essentials  of 
successful  sewage  purification  is  an  intermittent  application 
of  the  sewage  to  the  beds  in  which  bacteria  are  to  act.  This 
intermittent  action  is  secured  by  providing  a  small  additional 
tank  or  by  setting  aside  a  part  of  the  settling  tank  and  by 
installing  therein  some  kind  of  mechanism  for  the  purpose  of 
changing  the  more  or  less  regular  flow  into  an  intermittent  or 
periodical  flow.  The  proper  capacity  of  this  tank  will  be  con- 
sidered later  in  the  chapters  dealing  with  the  several  methods 
of  final  purification.  Now  it  may  be  said  only  that  the  size 
depends  on  the  amount  of  sewage  to  be  cared  for  per  day  and 
on  the  size  of  the  dose  demanded  by  the  purification  method. 
The  size  of  dose  depends  directly  upon  the  method  of  treatment 
and  on  the  size  of  the  particles  in  the  beds  intended  to  receive 
the  sewage.  On  sand  beds,  for  example,  it  is  customary  to 
discharge  the  sewage  from  the  dosing  tank  three  times  a  day, 
although  many  plants  operate  with  a  daily  discharge.  The  size 
of  the  dosing  tank,  however,  in  the  latter  case  has  to  be  three 
times  as  large  as  in  the  former,  and  it  is  usually  worth  while  to 
take  the  additional  trouble  of  having  more  frequent  operation 
in  order  to  save  the  cost  of  the  larger  tank. 

The  simplest  method  of  construction  of  the  dosing  tank 
is  to  make  it  a  part  of  the  sedimentation  tank  by  means  of  a 
cross  wall,  which  latter  must  be  strong  enough  to  withstand 
the  pressure  of  the  water  on  one  side  when  the  dosing  tank  is 
empty.  (See  Figs.  2  and  3.)  There  is  no  objection  to  this  tank 
being  separate  and  some  distance  away  from  the  sedimentation 

37 


38 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


tank,  and  sometimes,  for  convenience  in  distributing  the  sewage 
from  the  dosing  tank  onto  several  beds  in  turn,  the  dosing  tank 

is  placed  at  the  centre  of  a  group  of 
beds  with  the  settling  tank  outside. 
If  the  dosing  tank  is  a  part  of  the 
main  tank,  the  sewage  flows  into  it 
over  a  dividing  wall  between  the  two 
tanks  or  through  a  pipe  laid  through 
this  wall,  while  if  the  tank  is  separate 
from  the  other,  then  a  longer  pipe 
connection  is  required. 

It  is  economical  to  arrange  that 
the  level  of  the  sewage  in  the  dosing 
tank,  at  the  time  when  that  tank  dis- 
charges, shall  be  at  the  level  of  the 
sewage  in  the  settling  tank,  since  then 
no  head  is  lost.  It  is  better  still  to 
arrange  the  mechanism  in  the  dosing 
tank  so  that  the  level  of  the  sewage 
there  at  the  time  of  its  discharge  will 
be  from  four  to  eight  inches  higher 

than  the  normal  level  in  the  settling  tank.  The  effect  of 
this  is  to  back  up  the  sewage  and  raise  the  general  level  in 
the  settling  tank,  and  when  the  dosing  tank  discharges  there 
is  drawn  off  not  only  the  sewage  in  that  tank,  but  also  an 
amount  in  the  large  settling  tank  equivalent  to  that  which  is 
above  the  normal  level  of  the  sewage  there.  The  advantage  of 
this  is  plain  in  that  it  reduces  the  necessary  volume  of  the  dosing 
tank  by  that  of  the  back  water  in  the  settling  tank,  and,  while 
it  was  thought  at  one  time  that  such  a  frequent  variation  in 
the  level  of  the  main  tank  might  affect  injuriously  the  scum 
which  forms  there,  and  perhaps  also  the  bacterial  action  going 


FIG.  10. — Sludge  Valve  for 
Floor  of  Tank. 


VALVES,    SIPHONS,    AND   SIPHON   CHAMBERS 


39 


on  in  the  tank,  there  seems  to  be  no  real  reason  why  this 
method  may  not  be  used  with  considerable  advantage  in 
economy  of  construction. 

The  bottom  of  the  dosing  tank,  which  is  preferably  made 
of  concrete,  should  have  a  slope  toward  the  point  from  which 
the  outlet  pipe  leads,  thus  enabling  the  outward  rush  of  sewage 
to  carry  off  any  material  which  would  otherwise  settle  in  the 
bottom  and  perhaps  decompose  there. 

The  simplest  method  of  operating  the  dosing  tank  is  by 
means  of  a  hand  valve  fastened  either  to  the  floor  of  the  chamber 
or  to  the  bottom  of  the  outside  wall.  Fig.  10  shows  a  simple 
form  of  a  valve  suitable  for  the  floor 
and  intended  to  be  operated  by  a  rod 
extending  up  through  the  sewage 
to  the  outside  air.  Such  a  valve 
can  be  made  at  any  local  foundry, 
the  bearing  surfaces  turned  up  in 
any  machine  shop,  and  a  piece  of 
leather  for  packing  purchased  at  any 
hardware  store.  Such  a  design, 
however,  is  not  suitable  for  a  large 
valve  or  for  a  great  depth  of  water, 
since  the  pressure  on  the  valve  is  de- 
pendent on  the  weight  of  the  column 
of  water  acting  on  its  area.  If  the 
outlet  pipe  is  six  inches  in  diameter, 
the  diameter  of  the  upper  surface 
of  this  valve  would  be  about  ten 
inches,  and  the  area  of  the  top  of  the 
valve  would  be  about  half  a  square  foot,  so  that,  with  six  feet 
of  water  above,  weighing  62^  pounds  per  square  foot,  the  weight 
on  the  valve  to  be  lifted  would  be  186  pounds,  rather  more  than 


FIG.  1 1 . — Sludge  Valve  for 
Side  Wall  of  Tank. 


40 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


could  be  lifted  by  one  man.    Under  such  conditions  it  would  be 
necessary,  using  such  a  valve,  to  rig  a  lever,  the  fulcrum  being 

fastened  to  the  edge  of  the  tank,  the 
short  end  of  the  lever  to  the  rod,  and 
the  long  end  so  arranged  as  to  reduce 
the  load  in  the  ratio  of  about  one  to 
four.  Fig.  1 1  shows  another  type  of 
valve  intended  to  be  set  into  the  side 
of  the  tank  with  the  floor  sloping  rap- 
idly toward  the  low  point  at  which 
this  valve  is  set.  These  valves  require 
better  workmanship  and  are  prefera- 
bly purchased  from  one  of  the  dealers 
in  valves  who  make  this  type  as  one 
of  their  regular  stock  forms.  Fig.  12 
shows  the  design  made  by  the  Coffin 
Valve  Company,  of  Troy,  N.  Y.,  and 
a  similar  form  of  valve  is  made  by  the 
Caldwell  -  Wilcox  Company,  New- 
burgh,  N.  Y.  For  a 
six-inch  pipe,  these 

valves  are  so  made  that  the  danger  of  the 
moving  parts  rusting  together  is  avoided  by 
having  one  surface  bronze  or  some  similar  non- 
corrosive  metal.  Fig.  13  shows  an  ordinary 
gate  valve  generally  used  for  water  works,  but 
applicable  to  sewerage  works.  Such  a  valve 
is  shown  in  Fig.  5. 

Fig.  14  shows  a  form  made  in  England  and  FlG'  ^--Ordinary 

Gate  Valve. 

largely  used  as  a  cheap  valve  for  the    pur- 
pose of  emptying  a  tank  rapidly.    The  peculiarity  of  the  valve 
is  that  a  sidewise  motion  of  the  long  handle  locks  the  valve 


FIG.  12. — Sluice-Gate  Valve 
made  by  Coffin  Valve  Co. 


VALVES,    SIPHONS,    AND    SIPHON   CHAMBERS 


41 


into  position  so  that  the  moving  part   of   the   valve   may  be 
readily  set  at  any  height.    The  one  shown  in  the  figure  is  taken 
from  the  catalogue  of   the  Adams 
Hydraulic  Company,   Westminster, 
London,  and  is  listed  in  their  cata- 
logue at  $6.50  for  a  six-inch  pipe. 

Fig.  15  shows  another  type  of 
valve  which  is  supplied  by  some 
firms  making  sewer  pipe  and  con- 
sists, as  may  be  seen,  of  a  light 
moving  valve  which  is  attached  to 
a  projection  cast  on  the  top  of  the 
vitrified  tile  pipe  in  such  a  way  that 
the  valve  comes  to  an  even  seat  on 
the  bevelled  end  of  the  pipe.  It  is 
found  that  with  pressure  acting 
against  the  valve  the  thin  metal  of 
which  it  is  composed  is  pressed 
against  the  pipe  so  that  little,  if  any, 
water  or  sewage  will  escape.  The 
valve  can  easily  be  opened  by  at- 
taching a  cord  or  chain  to  the  ring  at  the  lower  edge  of  the 
valve,  and  when  released  the  valve  shuts  automatically.  This 
is  a  very  cheap  and  convenient  design,  and  answers  every 
purpose  for  emptying  tanks  by  hand. 

More  elaborate  structures  of  the  same  general  type  have 
been  made,  using  cast  iron  as  the  metal,  the  stationary  collar 
with  the  bevelled  end  being  built  into  the  masonry  wall  of  the 
tank.  This  type  of  flap  valve  is  faced  with  bronze,  and  the 
bearings  or  joints  have  bronze  bushings.  A  satisfactory  valve 
of  this  sort  can  be  made  at  a  local  foundry  and  machine  shop, 
but  there  is  danger  that  the  valve  will  not  be  water-tight.  Fig.  16 


FIG.  14. —  English  Slide  Valve 
with  Wedge-lock  Handle. 


42 


PRACTICAL    METHODS    OF    SEWAGE    DISPOSAL 


shows  such  a  valve  with  the  metal  seat  which  is  intended  to 
be  bolted  into  the  masonry  of  the  tank  wall. 

Fig.  1 7  shows  another  form  of  this  same  sort  of  valve,  taken 
from  the  catalogue  of  the  Adams  Hydraulic  Company,  and 
noteworthy  because  of  the  loose-link  connection  at  the  upper 
part  of  the  valve,  the  object  of  this  being  to  prevent  the  valve 
closing  at  the  upper  part  without,  at  the  same  time,  closing  at 
the  bottom. 


FIG.  15. — Flap  Valve  Attached  to  Length  of  Sewer  Pipe. 

If  the  dosing  tank  is  to  work  automatically  and  independ- 
ently of  human  agency,  an  arrangement  which  is  always  prefer- 
able, there  must  be  installed  some  mechanism  which  takes  the 
place  of  the  valve  operated  by  hand.  This  mechanism  is  in  almost 
every  case  a  siphon  which  is  put  into  action  when  the  water  level 
reaches  a  certain  height,  and  which  discharges  rapidly  until  the 
water  falls  to  a  point  when  air  is  admitted  to  the  inside  of  the 
siphon  pipe,  thereby  interrupting  the  flow. 


VALVES,    SIPHONS,    AND   SIPHON   CHAMBERS          43 

There  is  on  the  market  a  dosing  apparatus  which  does  not 
involve  a  siphon,  and  which  is  shown  in  Fig.  18.  This  is  made 
by  the  Ansonia  Manufacturing  Company,  30  Church  Street, 
New  York  City,  and  its  operation  may  be  described  as  follows: 
It  consists  of  two  floats  connected  by  means  of  a  chain  which 
passes  over  a  wheel  supported  in  the  upper  part  of  the  chamber. 
As  the  water  in  the  chamber  rises,  the  left-hand  float  shown 


FIG.  1 6. — Flap  Valve  with  Metallic  Seat  Attached. 

in  the  drawing  rises  and  the  right-hand  float  falls,  thereby 
communicating  a  rotary  motion  to  the  wheel.  A  projection  on 
this  wheel  at  a  certain  point  when  the  left-hand  valve  has 
reached  the  desired  height  communicates  with  an  inside  portion 
of  the  wheel,  to  which  a  chain  connected  with  the  valve  is 
attached.  Thus  the  valve  is  opened  at  the  right  height,  and 
remains  open  until  the  water  has  fallen  to  the  bottom  of  the 


44         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

chamber.  Then  the  left-hand  float  falls,  and  the  apparatus 
is  ready  to  repeat  the  operation.  This  apparatus,  for  a  small 
installation,  will  probably  cost,  set  up  in  place,  about  $15. 

Fig.  19  shows  the  simplest  form  of  siphon  arranged  to  dis- 
charge water  from  a  tank.  It  will  be  noticed  that  it  consists  of 
an  inverted  bent  pipe,  one  leg  being  longer  than  the  other, 
and  extending  into  a  pool  of  water  formed  in  the  end  of  the 


FIG.    17. — Flap  Valve  with  Loose-link  Hinges. 

discharge  pipe.  When  the  water  level  in  the  tank  reaches  the 
bent  portion  of  the  siphon  pipe,  the  water  begins  to  flow  out, 
and  will  continue  to  flow  until  air  is  drawn  in  at  the  lower  end 
of  the  short  leg.  This  stops  the  flow  and  the  tank  begins  to 
fill  again. 

Fig.  20  shows  another  method  of  working  the  siphon  and 
insuring  its   rapid  initial  action.     This  is  known  as  the  Van 


VALVES,    SIPHONS,    AND   SIPHON   CHAMBERS  45 

Vranken  flush  tank,  and  the  feature  of  this  arrangement  is 
the  movable  bucket,  which  in  one  position  seals  the  lower 
end  of  the  longer  leg.  Then,  however,  the  siphon  begins  to 
act,  and  the  bucket,  which  is  hung  on  trunnions,  is  disturbed 
and  its  contained  water  is  dumped  out.  This  allows  the  escape 
of  the  water  in  the  longer  leg  and  insures  a  vigorous  starting 
up  of  the  siphon  into  action. 


FIG.  1 8. — Intermittent  Dosing  Apparatus  made  by  Ansonia  M'f'g  Co. 

A  more  simple  type,  however,  is  the  inverted  siphon  arrange- 
ment, developed  perhaps  most  completely  by  the  Pacific  Flush 
Tank  Company  under  the  Miller  patents.  Fig.  21  shows  their 
ordinary  design,  the  upper  part  of  the  siphon  being  replaced  by  a 
bell  and  the  discharge  starting  when  the  level  of  the  water  in 
the  long  leg  of  the  siphon  has  been  depressed  sufficiently  to 
reach  the  curved  part  of  the  pipe.  The  principle  on  which  this 
siphon  works  is  as  follows: 

When  the  water  rises  in  the  tank  above  the  lower  edge 
of  the  bell,  the  air  which  remained  between  the  water  in  the 


46 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


siphon  pipe  and  in  the  bottom  of  the  tank  is  confined,  and,  as 
the  water  rises,  is  gradually  compressed.  The  effect  of  this 
compression  is  to  force  down  the  water  in  the  long  leg  of  the 
siphon  and  to  hold  down  the  level  of  the  water  inside  the  bell 
lower  than  the  level  outside.  When  sufficient  head  of  water 
in  the  tank  is  secured,  the  water  inside  the  pipe  will  be  forced 


FIG.  19. — Simplest  form  of  Automatic  Siphon. 

down  to  the  curved  part  of  the  pipe,  and,  the  siphon  being  so 
designed,  the  water  level  inside  the  bell  will  be  just  at  the 
top  of  the  same  pipe,  but  on  the  outside.  Any  slight  additional 
height  then  allows  the  contained  and  compressed  air  to  escape 
around  the  bend  in  the  pipe,  suddenly  relieving  the  pressure 
and  allowing  the  water  to  enter  the  pipe  from  under  the  bell 
readily.  Thus  the  siphon  starts  and  continues  to  flow  until 


VALVES,    SIPHONS,    AND    SIPHON    CHAMBERS          47 

the  water  level  falls  so  that  the  air  is  drawn  in  under  the  bell. 
That  stops  the  action  of  the  siphon  and  the  tank  fills  again. 
These  siphons  are  generally  sold  in  two  pieces,  the  cast  iron  bell 
and  the  curved  pipe  being  the  factory  product.  At  the  plant 


v» 

FIG.  20. — Van  Vranken  Automatic  Siphon. 

they  have  to  be  set  in  place,  generally  bedded  in  concrete  and 
properly  connected  with  the  outlet  pipe.  For  a  small  installa- 
tion a  three-inch  or  four-inch  siphon  is  ample,  and  will  cost, 
delivered,  from  $10  to  $15,  depending  on  the  freight. 

Fig.  22  shows  two  siphons  with  auxiliary  air-pressure  cham- 
bers installed  in  the  same  chamber  for  the  purpose  of  automati- 
cally diverting  the  flow  from  one  bed  to  another.  This  may  be 


48 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


done  more  simply  by  installing  two  ordinary  siphons  of  the 
Miller  or  similar  type.  If  one  of  these  siphons  is  filled  half  full 
when  the  tank  is  empty,  that  siphon  will  discharge  first  because 
-of  the  amount  of  water  already  present  in  the  U-shaped  tube. 
During  the  filling  of  the  tank  previous  to  its  discharge,  the 
other  siphon  will  partially  fill,  so  that  when  the  tank  begins 


FIG.  21. — Miller  Automatic  Siphon. 

to  fill  for  the  second  time  the  second  siphon  is  half  full  and  the 
first  nearly  empty.  In  this  way  alternate  action  is  secured  and 
the  discharge  takes  place  as  often  as  the  tanks  fill. 

Fig.  23  shows  three  similar  siphons  installed  with  some 
auxiliary  piping  attached  for  the  purpose  of  making  the  periodic 
discharge  more  positive.  These  small  auxiliary  pipes  are  so  put 
together  that  there  is  an  auxiliary  siphon  passing  under  the 


FIG.  22. — Double  Alternating  Siphons  of  the  Miller  Type. 


49 


50 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


edge  of  the  bells.  When  one  siphon  discharges,  the  auxiliary 
siphon  of  the  corresponding  large  siphon  is  filled  with  water, 
and  at  the  same  time  part  of  the  water  in  the  auxiliary  siphon 
of  the  other  is  discharged,  so  that  it  will  be  the  first  to  operate 


SECTION  A-B 
FIG.   23. — Triple  Alternating  Siphons  of  the   Miller  Type. 

at  the  next  filling.  When  the  water  is  forced  to  the  bottom  of 
the  small  siphon,  it  is  blown  out  through  the  vent  pipe,  and, 
the  air  following,  the  large  siphon  is  started. 

Fig.   24  shows  an  automatic  discharging  siphon  made  by 
the  Merritt  Company,  of  Camden,  N.  J.,  and  embodying  a 


VALVES,    SIPHONS,    AND   SIPHON   CHAMBERS          51 

different  principle.  The  main  discharge  pipe  is  built  in  the 
form  of  a  "U"  tube,  the  longer  leg  containing  an  auxiliary 
small  air  pipe,  with  a  return  bend  at  its  lower  end.  When  the 


FIG.  24. — Single  "Merritt"  Automatic  Siphon. 

chamber  starts  to  fill,  this  small  pipe  bend  or  seal  is  rilled  with 
water,  so  that  the  rising  water  confines  arid  compresses  air  in 
both  the  large  and  small  "U"  pipes.  In  time,  and  at  any 


52 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


desired  height,  determined  by  changing  the  relative  lengths  of 
the  parts  of  the  small  pipe  siphon,  the  seal  is  broken  and  the 
air  escaping  draws  air  enough  from  the  large  pipe  to  start  it 
in  action.  The  method  has  an  advantage  in  that  it  requires 


Bed.No.4 


Bed  No.3 


FIG.  25. — Air-lock  Siphon  for  Admitting  and  Releasing  Sewage  from  each 
one  of  Four  Beds  in  Regular  Order. 

no  deep  excavation,  and  the  mechanism  can  be  set  after  the 
siphon  chamber  is  built. 

Fig.  25  shows  a  method  of  securing  the  alternate  discharge 
of  sewage  by  siphons  whose  action  depends  upon  an  air  trap, 


VALVES,    SIPHONS,    AND   SIPHON   CHAMBERS          53 

each  siphon  being  of  the  type  shown  in  Fig.  24.  The  installation 
of  the  figure  is  further  complicated  by  the  fact  that  it  is  arranged 
to  discharge  sewage  from  the  four  contact  beds  as  well  as  to 
discharge  sewage  onto  the  beds.  The  compartments,  and  the 
piping  connected  therewith,  at  the  four  corners  operate  to 
admit  the  sewage  from  the  central  channel  onto  the  four  beds 
in  rotation.  The  four  square  wells  between  the  corner  wells 
operate  to  empty  those  beds  in  turn  into  the  pipe  shown  at  the 
centre  of  the  drawing,  the  pipe  leading  to  the  nearest  stream. 
The  operation  may  be  described  as  follows:  Sewage  enters  at 
the  top  of  the  drawing,  and  from  the  inlet  channel  flows  into 
the  siphon  channels  marked  A.  Ai  is  ready  to  discharge  if 
bed  No.  4  was  the  last  one  to  fill,  since,  when  that  bed 
filled,  the  small  bell  D4  forced  the  siphon  AI  open.  Sewage 
therefore  flows  through  siphon  Ai  into  bed  No.  i.  As  the 
sewage  level  rises  in  bed  No.  i,  the  outlet  siphon  from  bed  No.  2, 
G2,  is  locked  by  the  air  pipe  from  BI  so  that  bed  No.  2  will  be 
ready  for  the  next  dose.  Also  the  air  pipe  from  the  bell  Hi 
opens  the  siphon  G4,  and  allows  bed  No.  4  to  drain  into  the 
outlet  drain.  Also  bell  Di,  when  bed  No.  i  is  full,  opens  the 
siphon  A2  through  the  connecting  air  pipe  so  that  bed  No.  2 
begins  to  fill  as  soon  as  bed  No.  i  is  full.  And  finally  bell  Ci 
locks  the  siphon  Ai,  and  stops  further  flow  into  bed  No.  i.  The 
other  beds  operate  in  the  same  way  in  turn. 

The  manufacturers  of  siphons  are  always  glad  to  advise 
prospective  buyers  of  the  proper  arrangement  of  siphons  and  the 
details  of  placing,  with  dimension  sketches. 

As  a  summary,  it  may  be  pointed  out  that  in  any  installa- 
tion, one  of  the  three  methods  above  described  may  be  adopted. 

i.  A  simple  valve  worked  by  hand  may  b.e  adopted  and  the 
alternate  distribution  of  the  sewage  regulated  by  choice  of  the 
several  valves  placed  at  the  head  of  the  several  discharge  pipes. 


54          PRACTICAL    METHODS    OF    SEWAGE   DISPOSAL 

2.  An  automatic  discharge  mechanism  may  be  installed  which 
will   operate   regularly   and   intermittently,    but   lacking   any 
automatic  selection  of  the  bed  onto  which  the  discharge  is  to 
be  made.    These  siphons  will  discharge  as  often  as  the  tank  fills, 
but  the  particular  valve  must  be  opened  in  order  that  the  dis- 
charge may  take  place  onto  any  one  of  the  several  beds. 

3.  An  apparatus  may  be  installed  which  will  both  discharge 
intermittently  and  will  also  automatically  select  different  beds 
in  turn  onto  which  the  discharge  shall  take  place.    It  may  even 
discharge  onto  contact  beds  and  also  empty  those  beds,  entirely 
automatically. 

Which  of  these  mechanisms  shall  be  selected  depends  upon 
the  amount  of  money  available  and  on  the  value  to  be  placed 
on  the  freedom  from  constant  care  which  an  automatic  installa- 
tion gives.  Not  that  a  sewage-disposal  plant  may  be  ignored 
because  an  automatic  mechanism  has  been  installed.  No 
machine  is  infallible,  and  sewerage  machinery  may  give  out 
or  stop  working  just  as  that  for  any  other  purpose.  But  instead 
of  a  daily  routine  of  duties  which  may  not  be  interrupted,  by 
means  of  automatic  apparatus  one  may  avoid  everything  except 
casual  inspections  and  periodic  cleaning. 


CHAPTER  IV 
SUB-SURFACE  IRRIGATION 

The  disposal  of  sewage  by  the  method  of  sub-surface  irri- 
gation, sometimes  known  as  the  Waring  system,  consists 
in  its  distribution  by  means  of  open-jointed  tiling  over  a 
comparatively  large  area  of  soil  and  at  a  depth  of  a  few 
inches  beneath  the  ground  surface.  The  sewage  should  first 
be  passed  through  settling  tanks  to  remove  as  much  as  prac- 
ticable of  the  suspended  matters  contained  in  it,  as  explained 
in  the  chapter  on  settling  tanks.  The  partially  clarified  effluent 
from  the  settling  tank  should  then  be  collected  in  a  dosing  cham- 
ber, or  separate  compartment  of  the  settling  tank,  and  discharged 
intermittently,  preferably  by  means  of  a  siphon,  into  the  sub- 
surface irrigation  system.  This  intermittency  of  discharge  of 
accumulated  quantities  of  effluent  is  necessary  for  an  even 
distribution  of  the  effluent  throughout  the  entire  system  of 
sub-surface  tiling,  and  for  a  continuous  and  successful  opera- 
tion of  the  system  as  a  whole.  It  has  been  found  necessary, 
also,  to  alternate  the  discharge  of  effluent  from  the  dosing  or 
siphon  chamber  over  different  portions  of  the  irrigation  area. 
One  siphon  is  all  that  is  necessary  to  install  in  the  siphon  cham- 
ber for  sub-surface  irrigation  systems,  and  if  the  settling 
tank  has  two  compartments,  as  shown  in  Fig.  3,  Chapter 
II,  the  single  siphon  would  be  placed  in  the  centre  of  the 
chamber. 

The  principle  involved  in  this  method  of  sewage  purification 
is  that  of  any  general  method  of  sewage  reduction  in  whatever 
form  carried  on,  namely,  its  oxidation  or  nitrification.  This 
oxidation,  or  breaking  down  of  the  organic  matter  in  the  sewage, 
is  accomplished  in  this  case,  as  in  the  case  of  intermittent  sand 

55 


56         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

filters,  contact  beds,  and  sprinkling  filters,  through  the  agency 
of  bacterial  action. 

Householders  have  long  been  familiar  with  the  fact  that 
although  solids  contained  in  sewage  may  have  been  discharged 
for  long  periods  of  time  into  a  cesspool,  the  latter,  if  located 
in  dry,  porous  soil,  did  not  seem  to  become  filled  with  the  solid 
residue.  This  is  due  to  the  liquefaction  of  the  solid  matter  in 
the  sewage  after  its  discharge  into  the  cesspool,  and  to  the 
seepage  and  bacterial  reduction  of  the  liquid  matter  in  the 
surrounding  soil.  To  replace  the  cesspool  and  eliminate  the 
insanitary  conditions  which,  in  most  instances,  result  from  its 
use,  other  methods  have  been  devised  which  utilize  the  agencies 
of  nature  to  the  best  advantage.  Thus  the  sedimentation  and, 
in  some  cases,  the  liquefaction  of  the  solid  matters  in  sewage 
are  carried  on  in  specially  designed  settling  tanks  which  are 
easily  cleaned  and  which  provide  for  greater  efficiency  in  settling 
out  suspended  matters  than  the  cesspool.  Similarly,  the  filtra- 
tion of  liquids  from  cesspools  through  the  soil  is  replaced  by  the 
scientific  method  of  sub-surface  irrigation,  which  is  much  more 
efficient  in  three  distinct  ways:  (i)  the  limited  seepage  area 
represented  by  the  walls  of  the  cesspool  is  increased  many  times 
by  distributing  the  effluent  from  the  settling  tank  over  a  large 
area  of  soil  in  a  system  of  sub-surface  tiling;  (2)  the  bacterial 
reduction  is  more  effective,  since  it  has  been  found  that  the 
bacterial  action  necessary  to  purify  sewage  takes  place  in  the 
upper  layers  of  the  soil  and  is  almost  absent  at  depths  of  five  feet 
or  more;  (3)  the  soil  is  given  an  opportunity  to  rest  and  to  dry 
out  by  alternately  using  different  portions  of  the  sub-surface 
irrigation  system.  In  the  cesspool  the  seepage  of  the  effluent 
and  whatever  bacterial  action  takes  place  in  the  surrounding 
soil  must  go  on  continuously,  which  often  results  in  clogging  of 
the  soil  and  overflowing  of  the  cesspool. 


SUB-SURFACE   IRRIGATION  57 

The  purification  and  final  disposition  of  sewage  by  means  of 
sub-surface  irrigation  is  the  method  best  adapted  to  the  single 
residence,  and  oftentimes  to  the  hotel  or  institution,  if  soil 
conditions  are  favorable  and  proper  area  is  available.  This 
system  requires  less  oversight  in  its  operation  than  the  various 
forms  of  artificial  filters.  Furthermore,  the  sewage  is  entirely 
hidden  from  sight  after  it  leaves  the  settling  tank,  and  this  is 
usually  desirable  near  private  residences  and  on  the  grounds  of 
country  homes,  country  clubs,  and  summer  hotels.  Also, 
where  the  sewage  must  be  treated  in  close  proximity  to  a  resi- 
dence or  hotel  or  at  a  point  on  the  windward  side  of  a  residence, 
this  method,  more  effectually  than  any  other,  precludes  the 
possibility  of  a  nuisance  resulting  from  the  operation  carried  on, 
since  the  settling-tank  effluent  is  at  no  point  exposed  directly 
to  the  air.  Furthermore,  its  cost  is  less  than  that  of  other  works 
for  final  treatment  of  sewage,  and,  finally,  the  system  is  more 
easily  installed. 

The  method  is  in  reality  modified  broad  irrigation,  but  the 
sub-surface  irrigation  field  can  be  utilized  much  more  effectively 
and  with  considerably  less  attention  than  a  broad  irrigation 
area,  and,  as  noted  above,  is  less  liable  to  be  the  cause  of  a 
nuisance  or  to  be  the  means  of  spreading  infectious  disease 
through  the  agencies  of  flies  and  other  insects. 

If  an  area  of  sandy  soil  is  available  on  which  to  locate  the 
sub-surface  irrigation  field,  if  the  settling  tank  and  siphon 
chamber  have  been  correctly  built,  and  if  the  sub-surface  tiling 
system  has  been  properly  laid,  the  success  of  the  system  is  well 
assured.  On  the  other  hand,  failure  is  certain  if  either  broad 
irrigation  or  sub-surface  irrigation  methods  of  sewage  disposal 
are  attempted  on  stiff,  impervious  clay  soils.  Between  the 
ranges  of  porosity  of  soil  represented  by  these  limits  there  are 
many  soils  in  which  sewage  may  be  successfully  disposed  of 


58         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

by  sub-surface  irrigation.  A  sandy  or  gravelly  loam  will,  with- 
out question,  successfully  care  for  sewage  effluent  when  such 
effluent  is  properly  distributed  by  sub-surface  tiling,  and  even 
in  a  rather  heavy  soil  the  effluent  from  a  settling  tank  may  often 
be  disposed  of  satisfactorily  by  providing  for  a  greater  length  of 
sub-surface  tiling  per  person  served  by  the  settling  tank  than  that 
which  would  suffice  in  the  more  porous  soils.  However,  if  the 
soil  is  very  heavy  so  that  surface  water  does  not  readily  seep 
away,  or  if  the  ground-water  level  is  within  two  or  three  feet 
of  the  surface,  this  method  is  not  suitable  and  some  form  of 
filter,  described  in  the  succeeding  chapter,  should  be  used  for 
final  treatment  of  sewage. 

When  soil  conditions  and  the  area  available  are  favorable 
to  this  method  and  such  a  system  is  to  be  installed,  the  irriga- 
tion area  selected  should  be  at  the  point  where  the  ground-water 
level  is  lowest,  and  this  will  generally  be  on  a  plateau  or  bench 
at  the  head  of  a  slope  of  ground.  The  relative  elevation  of  the 
ground  surface  should,  of  course,  be  low  enough  to  insure 
operating  head  or  fall  to  operate  the  siphon  in  the  chamber 
adjoining  the  settling  tank  and  to  distribute  the  effluent  by 
gravity  to  the  sub-surface  tiling.  If  the  soil  is  composed  of  loose 
gravel,  or  lies  over  a  limestone  or  shale  formation,  the  location 
of  the  irrigation  area  should  be  selected  with  a  view  to  preventing 
the  contamination  of  any  wells  or  springs  which  may  exist  on 
the  premises, — that  is,  the  area  should  be  on  lower  ground, 
and  as  far  removed  from  wells  as  is  convenient. 

As  will  be  explained  later,  the  length  of  sub-surface  tiling 
necessary  to  receive  a  given  quantity  of  sewage  effluent  should 
vary,  within  certain  limits,  with  the  character  and  porosity  of 
the  soil,  thus  requiring  larger  quantities  of  effluent  to  be  deliv- 
ered from  the  siphon  or  dosing  chamber  in  the  case  of  the  more 
compact  soils.  Also  the  size  of  this  chamber  should  be  deter- 


SUB-SURFACE   IRRIGATION 


59 


TABLE  II 

FOR  USE  IN  THE  CONSTRUCTION  OF  SUB-SURFACE  IRRIGATION  SYSTEMS  IN  SANDY 

OR  VERY  POROUS  SOILS 
Dimensions  given  are  for  inside  measurement. 


No.  of  Persons  I 
Served  by 
Sewer. 

Total  Length  of 
3-inch  Sub- 
surface Tiling. 

No.  of  Sections 
in  Sub-surface 
System. 

Mean  Width  of 
Siphon  Chamber 
(Feet). 

Mean  Length  of 
Siphon  Chamber 
(Feet). 

Depth  of  Siphon 
Chamber  from 
Roof  of  Tank 
(Feet). 

Diameter  of 
Siphon  (Inches). 

Discharging 
Depth,  or  Maxi- 
mum Depth  of 
Effluent  above 
Lower  Edge  of 
Siphon  Bell 
(Inches). 

Distance  from 
Roof  to  Top  of 
Wall  between 
Settling  Tank  and 
Siphon  Chamber 
(Inches). 

4 

140 

2 

2' 

2' 

2'  4" 

3" 

13" 

12" 

8 

280 

2 

2'  6" 

2'  6" 

2'  4" 

3" 

13" 

12" 

12 

42O 

2 

2'  6" 

4' 

2f  4" 

3" 

13" 

12" 

15 

525 

2 

3'  6" 

4' 

2'  4" 

3" 

13" 

12" 

25 

875 

2 

3' 

4' 

3'  2" 

5" 

23" 

12" 

35 

1225 

2 

3'  8" 

4'  6" 

3'  2" 

5" 

23" 

12" 

50 

1750 

2 

4' 

6' 

3'  2" 

5" 

23" 

12" 

75 

2625 

2 

3' 

6' 

3'  2" 

5" 

23" 

16" 

100 

3500 

2 

4 

7' 

3'  2" 

5" 

23" 

16" 

125 

4375 

3 

5'  6" 

8' 

3'  2" 

5" 

23" 

16" 

150 

5250 

3 

7' 

8' 

3'  2" 

5" 

23" 

16" 

175 

6125 

3 

7'  6" 

8' 

3'  9" 

6" 

30" 

16" 

200 

7000 

3 

8' 

8' 

3'  9" 

6" 

30" 

1  8" 

TABLE  III 

FOR  USE  IN  THE  CONSTRUCTION  OF  SUB-SURFACE  IRRIGATION  SYSTEMS  IN 

HEAVIER  LOAMS  (NOT  CLAY  OR  HARDPAN) 
Dimensions  given  are  for  inside  measurements. 


THE 


No.  of  Persons 
Served  by 
Sewer. 

Total  Length  of 
3-Inch  Sub- 
surface Tiling. 

No.  of  Sections 
in  Sub-surface 
System 

Mean  Width  of 
Siphon  Chamber 
(Feet) 

Mean  Length  of 
Siphon  Chamber 
(Feet). 

Depth  of  Siphon 
Chamber  from 
Roof  of  Tank 
(Feet.) 

Diameter  of 
Siphon  (Inches). 

ac^1  QtiTiM  $ 
J^Q^S-S 

ifillP 
a|f§,§i 

Distance  from 
Roof  to  Top  of 
Wall  between 
Settling  Tank  and 
Siphon  Chamber 
(Inches). 

4 

300 

2 

2'    5" 

3' 

2'    4" 

3" 

13" 

12" 

8 

600 

2 

3' 

5' 

2'    4" 

3" 

13" 

12" 

12 

900 

2 

4' 

_r 

2'    4" 

3" 

13" 

12" 

15 

1125 

2 

4' 

6'  6" 

2'  4" 

3" 

13" 

12" 

25 

1875 

2 

4' 

6' 

3'  2" 

5" 

23" 

12" 

35 

2625 

2 

4' 

4'  6" 

3'  2" 

5" 

23" 

16" 

50 

3750 

2 

4'  6" 

6' 

3'  2" 

5" 

23" 

16" 

75 

5625 

2 

6' 

7' 

3'  2" 

5" 

23" 

16" 

100 

7500 

2 

7' 

8' 

3'  2" 

5" 

23" 

16" 

125 

9375 

3 

8' 

10' 

3'  9" 

6" 

30" 

20" 

150 

11250 

3 

9' 

12' 

3'  9" 

6" 

30" 

20" 

175 

13125 

3 

10' 

12' 

4'  2" 

8" 

35" 

20" 

200 

15000 

3 

ii' 

12' 

4'  2" 

8" 

35" 

20" 

60         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

mined  with  reference  to  the  number  of  sections  into  which  the 
sub-surface  tiling  system  is  divided. 

The  dimensions  of  siphon  chambers  to  effectively  deliver  the 
effluent  in  proper  volumes  to  the  sub-surface  irrigation  system 
are  given  in  the  following  tables,  which  indicate  widths  of  siphon 
chambers  to  agree  in  general  with  the  widths  of  the  settling 
tanks  to  serve  a  given  number  of  persons,  as  shown  in  Chapter  II. 
These  tables  of  dimensions  for  siphon  chambers  provide  for  two 
different  capacities  where  the  same  number  of  persons  are 
served  by  the  sewer,  depending  on  the  total  lengths  of  sub- 
surface tiling  required,  which  in  turn  depend  on  the  character 
of  the  soil  in  which  the  sub-surface  system  is  laid.  The  tables 
provide  for  a  division  of  the  sub-surface  tiling  system  into  two 
parts  up  to  a  system  for  100  persons,  and  into  three  parts  for 
a  greater  number  of  persons.  These  tables  also  show  the  total 
length  of  lateral  distributing  tiling  in  the  sub-surface  irrigation 
system  necessary  to  distribute  over  a  sufficient  area  at  the 
irrigation  field,  in  both  sandy  soils  and  in  the  heavier  loams, 
the  various  quantities  of  sewage  to  be  treated  in  the  different- 
sized  tanks  and  discharged  from  the  siphon  chambers.  The  tables 
also  indicate  the  diameter  of  the  siphon  and  the  discharging 
depth  of  each  siphon. 

As  discussed  in  Chapter  III,  the  siphon,  in  discharging, 
may  draw  upon  the  upper  4  to  8  inches  of  sewage  in  the 
settling  tank  without  interfering  with  the  efficiency  of  the 
tank.  The  dimensions  of  siphon  chambers  for  75  or  more  per- 
sons in  Table  II,  and  for  35  or  more  persons  in  Table  III  (see 
page  59) ,  provide  for  such  a  draught  upon  the  settling- tank  con- 
tents of  from  4  to  8  inches  when  the  siphon  discharges.  This  will 
decrease  the  cost  of  the  plant  somewhat  and  provide  for  a  more 
efficient  form  of  siphon  chamber.  The  last  column  in  each  table 
provides  for  the  proper  height  of  dividing-wall  between  the 


00 


62 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


settling  tank  and  siphon  chamber  to  allow  the  drawing  down 
of  the  settling-tank  contents  as  noted  above. 


FIG.  27. — Plan  and  Section  of  a  Portion  of  a  Sub-surface  Irrigation  System. 

The  sub-surface  irrigation  or  distributing  system  consists 
of  a  main  carrier  or  effluent  sewer  leading  away  from  the  siphon 


SUB-SURFACE   IRRIGATION  63 

chamber  to  the  irrigation  field,  of  two  or  more  branches 
of  this  main  carrier,  and  of  parallel  lines  of  lateral  distributing 
tiling  extending  at  intervals  of  4  to  6  feet  from  the  branch 
carriers,  or,  in  some  locations,  from  each  side  of  the  branch 
carriers. 

The  frontispiece  shows  the  relation  between  the  several 
portions  of  a  sub-surface  irrigation  system.  The  house  sewer  is 
shown  leading  to  the  settling  tank,  and  from  the  siphon  chamber 
adjoining  the  settling  tank  the  main  carrier  or  effluent  sewer 
is  shown  leading  to  a  diverting  manhole  from  which  the  effluent 
is  carried  at  each  discharge  of  the  siphon  to  the  lateral  lines  of 
sub-surface  tiling  by  the  two  branch  carriers. 

Fig.  26  shows  in  plan  and  section  a  sub-surface  irrigation 
system.  The  section,  which  is  drawn  to  a  larger  scale  than  the 
plan,  shows  the  settling  tank  and  the  adjoining  siphon  chamber. 
From  this  siphon  chamber  the  effluent  sewer  carries  the  discharge 
from  the  siphon  to  the  diverting  manhole,  at  which  point  the 
effluent  is  diverted  to  the  different  portions  of  the  sub-surface 
tiling. 

In  Fig.  27  is  shown  in  plan  the  diverting  manhole  and  a 
small  portion  of  the  sub-surface  tiling  system  together  with  a 
section  through  the  diverting  manhole  and  one  of  the  lines  of 
distributing  tiling. 

The  main  carrier  should  be  of  vitrified  tile  sewer  pipe  with 
cemented  joints,  and  should  always  have  two  or  more  branches 
at  the  irrigation  field  in  order  to  allow  the  use  of  different  por- 
tions of  the  field  in  turn  for  three  days  or  a  week  at  a  time, 
thus  allowing  one  of  the  portions  of  the  field  to  be  resting  for 
corresponding  periods.  The  branch  carriers  should  be  of  vitri- 
fied tile  also,  and  should  have  cemented  joints.  If  the  diameter 
of  the  siphon  is  5  inches,  the  main  carrier  should  be  of  8-inch 
vitrified  tile  with  a  fall  of  at  least  6  inches  per  100  feet 


64        PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

in  order  to  quickly  carry  the  dose  from  the  siphon  chamber  to 
the  several  lines  of  sub-surface  tiling  forming  the  distributing 
system.  With  3 -inch  siphons,  a  6-inch  main  carrier  may 
be  used,  but  the  gradient  or  fall  of  the  main  carrier  should 
then  be  at  least  12  inches  per  100  feet,  owing  to  the  smaller 
capacity  of  the  6-inch  pipe.  In  placing  the  siphon  in  posi- 
tion, when  the  siphon  chamber  is  being 
built,  care  should  be  taken  to  see  that 
the  trap  or  U-shaped  pipe  is  set  plumb 
FIG.  28.— Y-Branch  of  or  jn  a  vertical  position.  Concrete 

Vitrified  Tile  Pipe.  111,1         i         i        j  j  ,,        •    i 

should  then  be  placed  around  the  siphon 

to  hold  it  in  proper  position  and  at  the  proper  height,  and 
the  trap  should  be  filled  with  water  before  the  bell  is  placed 
in  position.  The  bell  should  then  be  placed  in  position  over  the 
long  leg  of  the  trap  to  prevent  the  materials  used  in  construction 
from  being  dropped  into  the  siphon.  The  siphon  should  be 
set  so  that  the  lower  edge  of  the  bell,  or  of  that  portion  of 
the  bell  under  which  the  effluent  is  to  flow,  is  three  inches 
above  the  floor  of  the  siphon  chamber. 

In  laying  the  distributing  system,  every  second  or  third 
length  of  the  branch  carriers,  according 
to  the  porosity  of  the  soil  and  the  spa- 
cing of  the  lines  of  distributing  tiling, 
should  consist  of  a  Y-branch  (see  Fig. 
28),  to  which  a  one-eighth  bend  (see  Fig.  FIG.  29.— Eighth  Bend  of 
29)  should  be  fitted  if  the  lines  of  lateral  Vitrified  Tile  Pipe, 
tiling  are  to  be  laid  at  right  angles  to  the  main  carriers,  as 
shown  in  Fig.  27;  or  the  lateral  tiling  may  be  fitted  directly  to 
the  Y-branch  if  the  lateral  lines  are  to  be  led  away  from  the 
carrier  at  an  angle  of  45°,  as  shown  in  Fig.  30.  The  Y  should 
branch  from  the  lower  portion  of  the  pipe,  as  shown  in  Fig.  28. 

The  lateral  tiling  should  be  of  three-inch  agricultural  tile 


FlG.  30. — Sub-surface  Tiling. 


66          PRACTICAL    METHODS    OF    SEWAGE    DISPOSAL 

(see  Fig.  31),  laid  with  a  space  of  one-quarter  inch  between  each 
length  and  with  a  piece  of  tar  paper  or  a  half-collar  of  larger 
diameter  pipe,  as  shown  in  Fig.  32,  placed  over  the  joints  to 
prevent  clogging  of  the  pipe  with  earth.  In  the  heavier  soils  the 
lateral  lines  of  sub-surface  tiling  are  sometimes  set  in  trenches 
eight  to  fourteen  inches  deep  and  about  twelve  inches  wide, 
filled  with  broken  stone  or  gravel  placed  around  the  tiling  to 
within  two  or  three  inches  of  the  ground  surface,  as  shown  in 
Fig.  32.  This  allows  the  effluent  to  seep  away  more  readily,  but 
while  of  advantage  in  those  soils  the  provision  is  not  necessary 
in  the  more  porous  soils. 


FIG.  31. — Photograph  of  Tile  laid  as  if  for  Sewage  Disposal. 

It  is  generally  found  that  a  sufficient  length  of  sub-surface 
tiling  should  be  laid  to  provide  for  not  more  than  one  to  three 
gallons  of  effluent  per  day  for  each  linear  foot  of  tiling.  In 
sandy  soils  there  should  be  at  least  thirty  to  forty  feet  of  tiling 
for  each  person  served  by  the  sewer,  with  six  feet  of  space 
between  the  lines  of  tiling.  This  length  per  person  should 
be  increased  up  to  seventy  or  eighty  feet  for  the  more  compact 
sandy  or  gravelly  loams,  or  the  lighter  clay  loams,  with  the 
lateral  tiling  spaced  four  feet  apart.  It  is  not  considered  feasible 
to  attempt  to  dispose  of  sewage  by  sub-surface  irrigation  in 
soils  which  will  not  care  for  effluent  when  the  greater  lengths 
of  tiling  per  person,  as  stated  above,  will  not  prevent  the  appear- 


SUB-SURFACE   IRRIGATION 


67 


ance  of  effluent  on  the  surface.  If,  however,  after  the  installa- 
tion of  a  sub-surface  system  in  a  rather  heavy  soil,  it  is  found 
that  proper  seepage  of  the  effluent  does  not  occur,  the  lateral 
branches  may  sometimes  be  lengthened  and  the  system  then 
found  to  operate  satisfactorily. 

The  lines  of  lateral  tiling  should  be  laid  with  the  invert,  or 
bottom  of  the  pipe,  inside,  from  six  inches  to  one  foot  below  the 
surface,  as  shown  in  Fig.  27.  They  should  be  parallel  with  the 
contours  or  at  right  angles  with  the  slope  of  the  field,  and  should 


FIG.  32. — Sub-surface  Tiling  with  Broken  Stone  or  Gravel  Surrounding  Pipe. 

have  a  gradient  or  fall  of  one-sixteenth  of  an  inch  to  the  foot 
when  laid  in  sandy  soil  or  sandy  loam,  and  of  not  more  than 
one  thirty-second  of  an  inch  to  the  foot  when  laid  in  the  heavier 
loams.  To  obtain  such  gradients  for  the  sub-surface  tiling  it  is 
sometimes  necessary  to  lay  out  the  trenches  along  irregular  or 
curved  lines,  as  shown  in  Fig.  33.  The  tiling  should  be  laid 
near  the  surface,  as  stated,  and  never  deeper  than  twelve  inches. 
The  temperature  of  the  sewage  will  prevent  its  freezing  even  in 
very  severe  winter  weather,  especially  when  the  ground  is 
covered  with  snow. 


68         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

To  provide  for  diverting  the  flow  from  the  siphon  chamber 
first  into  one  of  the  two  portions  into  which  the  sub-surface  sys- 
tem is  divided,  and  then,  after  an  interval  of  three  days  or  a 
week,  into  the  other  portion  of  the  system,  at  the  point  where 
the  main  carrier  is  to  branch,  a  ten-inch  iron  pipe  casting  (see 
Fig.  34) ,  with  its  lower  portion  forming  the  body  of  a  double  Y- 
branch  of  six-inch  or  eight-inch  pipe,  may  be  placed,  having  a 
swinging  blade  or  gate  attached  inside  in  a  vertical  position. 
When,  for  example,  the  effluent  has  been  passed  for  a  week 
into  section  B  of  the  sub-surface  system,  the  gate  C,  shown  in 
ig.  34,  may  be  swung  to  the  dotted  position  and  the  effluent, 


FIG.  33. — Sub-surface  System  on  Irregular  Ground. 

at  each  discharge  of  the  siphon  chamber,  will  then  pass  through 
the  branch  carrier  A  to  section  A  of  the  sub-surface  system; 
or  a  double  Y-branch  of  iron  pipe  (see  Fig.  35)  or  a  cross  may  be 
placed  at  this  point  on  the  main  carrier  when  there  are  to  be 
three  sections  of  the  sub-surface  system,  and  valves  may  be 
placed  on  the  three  branches  of  the  main  carrier  thus  formed 
to  permit  of  alternately  shutting  off  the  flow  to  the  various 
sections  of  the  sub-surface  tiling  system  (see  also  Fig.  30). 
Perhaps  the  simplest  and  most  serviceable  device,  however, 
for  alternately  resting  different  portions  of  the  irrigation  field 
is  a  diverting  manhole  with  stop  planks  or  wooden  sluices 


SUB-SURFACE   IRRIGATION  69 

sliding  in  grooves  in  the  concrete  walls  or  in  a  wooden  frame, 
as  shown  in  Fig.  27.  (See  also  Fig.  43,  Chapter  V.) 

Where  the  ground-water  level  is  not  very  deep  below  the 
surface,  or  a  clay  or  hardpan  stratum  occurs  at  a  depth  of  a  few 
feet,  it  is  advisable  to  underdrain  the  irrigation  field  by  lines 
of  open-jointed  tiling  laid  at  right  angles  to  the  lateral  dis- 
tributing tiling  and  spaced  about  fifteen  feet  apart.  (See  Fig.  36.) 

These  underdrains  should  be  placed  at  least  four  feet  below 


FIG.  34. — Special  Casting  of  Double  Y-Branch  with  Swinging  Gate. 

the  surface,  and  inspection  pipes  should  be  placed  over  the  outlets 
of  the  underdrains  or  at  the  points  where  they  discharge  into  a 
main  underdrain,  in  order  to  afford  opportunity  to  determine  if 
all  portions  of  the  irrigation  field  are  properly  caring  for  the 
effluent.  To  provide  for  the  placing  of  the  inspection  pipes, 
a  length  of  vitrified  tile  with  a  Tee  may  be  placed  on  each  line 
of  underdrain  tiling  near  its  junction  with  the  main  underdrain. 
On  this  Tee,  two  or  three  lengths  of  vitrified  tile  may  be  set, 


70 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


reaching  to  the  ground  surface  and  provided  with  a  removable 
wooden  cover  or  a  vitrified  tile  cap.  This  provision  for  inspec- 
tion is  necessary  where  underdrains  must  be  laid  and  where 
the  pollution  of  a  stream  is  to  be  prevented,  since  it  is  often 
found  that  through  the  activities  of  burrowing  animals  direct 
outlets  from  the  distributing  tiling  to  the  underdrains  are  formed 


FIG.  35. — Double  Y-Branch  with  Valves  on  Branches  of  Main  Carrier. 

and  the  final  effluent  is  therefore  not  sufficiently  purified  by 
seepage  through  the  soil.  It  is  desirable  for  this  reason  to 
omit  the  underdrains  when  possible,  and  in  some  instances  a 
blind  ditch  may  be  constructed  around  two  or  three  sides  of 
the  field  in  order  to  intercept  the  ground-water  flow  and  to 
lower  the  ground-water  level  at  the  field,  thus  better  insuring 


SUB-SURFACE   IRRIGATION 


71 


proper  seepage  of  the  effluent  distributed  by  the  sub-surface 
tiling. 

The  essential  features  of  the  sub-surface  irrigation  system 
of  sewage  disposal  have  been  outlined  above,  and  it  may  be  said 
that  this  method  is  especially  adapted  to  the  residence  or  single 
house.  The  method  may  be  employed  with  success  to  dispose 
of  sewage  from  country  clubs  and  summer  hotels,  provided  the 
soil  conditions  are  favorable  and  proper  areas  may  be  utilized. 
In  these  cases  the  comparatively  short  period  during  each  year 
in  which  the  system  is  in  use  and  the  resulting  long  periods 

in 


r 

T 

I      t 

t 

:            r 

r 

•            r 

1 

t 

! 

( 

! 

I 

! 

I 

i 

{ 

I 

! 

i 

v       i 

i 

] 

-i 

i      ~I 

| 

4 

\{ 

o!| 

FIG.   36. — Sub-surface   Tiling   System   with   Underdrains. 

of  rest  give  opportunity  for  a  recuperation  of  the  soil  and  per- 
mit the  use  of  this  system  in  comparatively  large  installations 
where,  under  continuous  operation,  a  different  method  of  dis- 
posal would  be  indicated.  It  should  be  borne  in  mind,  how- 
ever, that  when  any  doubt  arises  as  to  the  suitability  of  the  soil 
to  care  for  sewage  by  this  method,  and  especially  where  con- 
siderable expense  would  be  involved  in  the  installation  of  the 
system,  competent  engineering  advice  should  be  sought  by 
property  owners  before  the  installation  is  undertaken.  In  fact, 
it  is  advisable  in  the  case  of  all  large  plants  of  this  type  to  employ 


72         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

the  services  of  a  sanitary  engineer  to  lay  out  the  system,  since 
the  matter  of  accurate  gradients  and  proper  operating  arrange- 
ments then  becomes  very  essential  to  the  success  of  the  under- 
taking. 

While  it  is  not  generally  advisable  to  arrange  for  the  dis- 
posal of  sewage  by  sub-surface  irrigation  when  the  number  of 
persons  served  by  the  sewer  exceeds  two  hundred,  this  method 
will  be  found  a  most  satisfactory  one  if  the  general  conditions 
at  any  point  are  favorable  to  its  use  as  heretofore  described, 
and  in  such  cases  the  adoption  of  this  system  is  strongly  recom- 
mended to  the  owners  of  residences,  summer  camps,  summer 
hotels  and  boarding-houses,  and  to  the  managers  of  moderate- 
sized  institutions  and  of  country  clubs  who  must  meet  the 
problem  of  properly  disposing  of  sewage  on  their  own  premises. 


CHAPTER  V 
SEWAGE  FILTERS 

It  has  been  shown  that  the  selection  of  the  type  of  plant  best 
suited  to  solve  the  sewage-disposal  problem  at  any  given  place 
depends  on  several  factors  and  can  be  safely  made  only  after 
a  consideration  and  study  of  such  local  conditions  as  the  char- 
acter of  the  soil,  the  area  available,  the  presence  and  nearness 
to  the  surface  of  ground  water,  and  the  local  topographical 
conditions.  If  sub-surface  irrigation  is  not  feasible,  when,  for 
instance,  the  soil  is  nearly  impervious  to  water  or  when,  in 
the  case  of  a  wet  soil,  adequate  underdrainage  is  not  possible, 
some  form  of  artificial  filter  must  be  constructed  to  complete 
the  reduction  of  the  sewage  where  the  effluent  from  the  settling 
tank  may  not  properly  be  discharged  directly  into  a  stream. 

If  such  a  filter  is  to  be  constructed,  the  kind  most  suitable 
depends,  in  turn,  upon  several  factors,  such  as  the  degree  of  puri- 
fication to  be  attained,  the  suitability  of  the  available  areas 
or  locations  for  the  different  types  of  filters,  the  operating 
head  or  fall  available,  and  the  relative  cost  of  the  sand,  gravel, 
broken  stone,  or  furnace  slag  which  may  be  used  as  material 
for  the  filter  bed. 

With  respect  to  the  degree  of  purification  of  sewage  that  is 
desired  it  may  be  said  that,  of  the  three  general  methods  of 
sewage  purification,  namely,  intermittent  sand  filtration,  treat- 
ment in  contact  beds,  and  filtration  through  sprinkling  or 
trickling  filters,  the  first  method  produces  the  most  highly 
purified  effluent.  Such  an  effluent,  if  from  a  properly  con- 
structed and  operated  sand  filter,  may  generally  be  considered 
sufficiently  purified  to  allow  its  discharge  into  a  stream,  even  if 

73 


74         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

the  stream  is  subsequently  used  as  a  source  of  potable  water 
supply.  In  some  instances,  however,  subsequent  sterilization 
or  disinfection  of  the  effluent  may  be  required,  particularly  if 
the  waterworks  intake  is  relatively  near  the  point  of  discharge 
from  the  sewage  filter,  or  if  the  flow  of  the  stream  is  small  in 
comparison  with  the  sewage  flow.  However,  if  a  stream  used 
as  a  source  of  potable  water  supply  receives  the  effluent  from 
a  properly  operated  sand  filter,  the  further  safeguarding  of  the 
quality  of  the  water  should  generally  be  accomplished  by 
nitration  or  sterilization  of  the  water  supply,  or  both. 

In  many  cases  the  local  conditions  are  such  that  contact 
beds  or  sprinkling  niters  may  be  constructed  more  easily  or 
more  economically  than  sand  filters  and,  at  the  same  time,  the 
lesser  efficiency  of  the  contact  bed  or  the  sprinkling  filter,  owing 
to  the  fact  that  the  stream  is  not  used  for  water  supply,  may 
not  preclude  the  adoption  of  these  latter  types  of  plants. 

However,  where  natural  deposits  of  sand  of  not  too  finely 
divided  particles  occur  or  where  such  sand  may  be  readily  pro- 
cured, intermittent  sand  filters  are  most  satisfactory  for  the 
final  treatment  of  sewage. 

INTERMITTENT  SAND  FILTERS 

The  agencies  employed  in  purifying  sewage  by  intermittent 
sand  filtration  involve  its  oxidation,  or  nitrification  by  bacterial 
action,  while  the  mechanical  straining  effected  by  its  passage 
through  the  sand  plays  a  very  small  part  in  its  reduction: 

Where  natural  deposits  of  sand  of  suitable  quality  occur, 
sand  filters  are  constructed  by  levelling  off  definite  areas  of 
sand  and  making  embankments  eighteen  inches  high  to  enclose 
these  areas,  the  embankments  being  generally  formed  of  the 
surface  loam  and  subsoil  which  must  usually  be  removed  in 


SEWAGE   FILTERS 


75 


order  to  expose  the  sand  layer.  There  should  be  from  three  to 
five  beds  prepared  in  order  to  provide  for  alternating  the  dis- 
charge of  the  effluent  from  the  settling  tank  over  different 
portions  of  the  filtration  area  and  thus  to  provide  resting  periods 
for  each  bed  while  in  operation.  Also,  the  preparation  of  several 
equal  areas  permits  discontinuing  the  use  of  any  single  area 
for  several  days  or  a  week  at  a  time  in  order  to  allow  it  to  dry 
out  and  permanently  retain  its  filtering  capacity.  In  Fig.  37 


FIG.  37. — View  of  Sand-filter  Beds  for  Village  in  Massachusetts. 

is  shown  a  view  of  a  set  of  sand-filter  beds  arranged  in  terraces 
on  sloping  ground,  the  embankments  being  formed  by  the 
material  excavated  to  uncover  the  natural  sand  layer. 

The  proper  number  of  beds  and  the  area  of  each  bed  corre- 
sponding to  the  number  of  persons  to  be  served  by  the  sewer 
are  given  in  Table  IV.  This  table  also  gives  the  required  dimen- 
sions of  siphon  chambers  (assuming  that  this  chamber  forms 
a  separate  compartment  of  the  settling  tank)  for  the  capacities 
necessary  in  order  that  the  effluent  may  be  distributed  in  proper 


76 


PRACTICAL    METHODS    OF    SEWAGE    DISPOSAL 


quantities  over  each  bed  or  over  each  pair  of  beds,  as  in  the 
case  of  plants  serving  two  hundred  or  more  persons.  The 
widths  of  siphon  chambers  given  correspond  in  general  with 
the  widths  of  settling  tanks  given  in  Table  I.  As  in  Table  3, 
the  dimensions  of  siphon  chambers  given  are  based  on  a  drawing 
down  of  the  effluent  in  the  tank  when  the  siphons  discharge, 
amounting  to  from  four  to  eight  inches.  The  last  column  in 

TABLE   IV 
FOR  USE  IN  CONSTRUCTING  INTERMITTENT  SAND  FILTERS 


Persons 
Served  by 
Sewer. 

No.  of 
Beds. 

Area  of 
Each  Bed 
(Square  Feet). 

Mean  Width 
and  Length 
of  Siphon 
Chamber 
(Feet). 

Diameter 
of  Siphon 
(Inches). 

Distance  from  Roof 
of  Settling  Tank  to 
Top  of  Wall  between 
Settling  Tank  and 
Siphon  Chamber 
(Inches). 

4 

3 

60 

3X3 

3 

12 

8 

3 

120 

3X5 

3 

12 

12 

3 

180 

4X5 

3 

12 

15 

3 

224 

4     x    6.5 

3 

12 

25 

3 

350 

4x6 

5 

12 

35 

3 

480 

4-5x    5 

5 

16 

50 

3 

660 

5x6 

5 

16 

75 

3 

1000 

6x7 

5 

18 

IOO 

3 

1320 

7     x    8 

5 

18 

125 

3 

1660 

5-5x    8 

6 

20 

150 

3 

2000 

8x8 

6 

20 

i?5 

3 

2330 

8x9 

6 

20 

200 

5 

1600 

8        X  12 

8 

20 

250 

5 

2000 

10.  5x  12 

8 

20 

300 

5 

2400 

12        X  13 

8 

20 

350 

5 

2800 

13     xi4 

8 

20 

4OO 

5                3200 

13     xi7 

8 

20 

450 

5 

3600 

13     XIQ 

8 

20 

500 

5                4000 

13       X2I 

8 

2O 

the  table  gives  the  space  which  should  be  left  between  the  roof 
of  the  tank  and  the  top  of  the  dividing  wall  between  the  settling 
tank  and  the  siphon  chamber  to  provide  for  this  draught  upon 
the  settling- tank  contents.  It  will  be  seen  that  no  draught 
upon  the  contents  of  the  settling  tank  when  the  siphons  dis- 
charge is  arranged  for  in  the  case  of  tanks  serving  from  four  to 
twenty-five  persons. 


SEWAGE    FILTERS 


77 


The  siphons  in  each  instance  should  be  so  placed  that  the 
lower  edge  of  the  bell  of  the  siphon  will  be  at  a  distance  below 
the  roof  of  the  tank  equal  to  twelve  inches  plus  the  drawing 
depth  or  discharging  depth  of  a  siphon  of  the  diameter  indicated. 
There  should  be  three  inches  of  space  between  the  siphon  bell 
and  the  floor  of  the  chamber.  The  discharging  depths  of  siphons 
as  used  in  forming  Tables  2,  3,  4,  and  5  are  as  follows: 


Diameter  of  Siphon. 
3  inches 

5 

6 

8 

10 

12 


Discharging  Depth. 
13  inches 
23 
30 
35 
60 
72 


If  the  siphons  installed  are  larger  or  smaller  than  those 
shown  in  these  tables,  or  if  the  particular  make  of  siphon  pur- 
chased has  the  same  diameter  but  a  different  discharging 
depth,  proper  allowance  must  be  made  in  proportioning  the 
size  of  the  dosing  chamber. 

In  order  to  quickly  convey  the  dose  from  the  siphon  chamber 
to  the  filter  beds  at  the  rate  at  which  the  siphon  discharges, 
the  sewer  from  the  siphon  chamber  should  be  of  proper  size 
and  should  have  a  sufficient  gradient.  For  instance,  with  a 
3-inch  siphon  the  sewer  should  be  6  inches  in  diameter,  with  a 
gradient  or  fall  of  at  least  12  inches  per  100  feet;  with  a  5-inch 
siphon,  the  sewer  should  be  8  inches  in  diameter,  with  a  gradient 
of  at  least  6  inches  in  100  feet;  with  a  6-inch  siphon,  the  diameter 
of  the  sewer  should  be  8  inches,  and  should  have  a  gradient  of 
at  least  12  inches  per  100  feet,  or  10  inches  with  a  gradient  of 
at  least  3  inches  per  100  feet;  with  an  8-inch  siphon,  12  inches, 
with  a  gradient  of  at  least  12  inches  per  100  feet. 

Sewage  is  sometimes  applied  directly  to  the  beds  without 
treatment  in  settling  tanks,  generally,  in  such  cases,  after  having 


78 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


been  screened  to  remove  the  larger  suspended  matters,  but  it  is 
decidedly  preferable  in  the  case  of  the  smaller  plants  under 
discussion  to  pass  the  sewage  first  through  settling  tanks,  as  in 
the  method  of  sub-surface  irrigation.  Therefore,  the  areas  of 
beds  given  in  the  table  are  for  sewage  which  has  been  passed 
through  settling  tanks.  It  is  even  necessary,  in  the  case  of 
sand  filters  for  institutions  where  considerable  grease  and  soaps 
are  contained  in  the  sewage,  to  provide  grease  traps  through 
which  the  sewage  must  pass  before  it  reaches  the  settling  tank. 
The  effluent  from  the  tank  should  be  discharged  intermit- 


Trough 


,Sewer  from  Residence 


Settling  Tank.' 

Siphon  Chamber 


•Underdrains 


FIG.  38. — Layout  for  Intermittent  Sand  Filtration. 


tently  by  means  of  a  dosing  chamber  and  siphon  and  should 
be  distributed  quickly  over  the  surface  of  the  bed  as  uniformly 
as  possible.  This  is  generally  accomplished  in  the  case  of 
the  larger  beds  by  laying  on  the  surface  of  the  bed,  wooden 
troughs,  with  short  branches,  as  shown  in  Figs.  38  and  39. 
A  detail  of  a  portion  of  these  distributing  troughs  is  given  in 
Fig.  40.  This  view  shows  the  hinged  gates  which  are  used 
to  effect  a  proportionate  division  of  the  flow  of  the  various 
branches  of  the  main  trough.  The  view  also  shows  the  slots 
in  the  sides  of  the  troughs  which  allow  the  sewage  to  flow  out 
onto  the  bed. 


SEWAGE    FILTERS 


79 


If  the  ground-water  level  is  within  three  feet  of  the  surface 
at  any  time,  or  if  the  sand  is  very  fine  and  contains  a  slight 
proportion  of  clay,  underdrains  should  be  laid  at  depths  of  four 
feet  to  prevent  the  beds  from  becoming  waterlogged. 

Where  sand  deposits  do  not  occur  at  a  point  suitable  for 
the  location  of  the  disposal  plant,  but  where  sand  may  be  pro- 
cured at  a  reasonable  cost,  the  beds  may  be  formed  artificially 


FIG.  39. — Intermittent  Sand-filtration  Beds. 

similar  to  the  natural  sand  beds  heretofore  described,  but  should 
not  be  less  than  three  feet  deep.  It  is  generally  necessary  in  the 
case  of  artificially  constructed  sand  filters  to  provide  under- 
drains as  described  below. 

Two  views  of  such  an  artificial  sand  filter  are  shown  by 
Figs.  41  and  42.  In  Fig.  41  the  settling  tank  and  siphon  chamber 
may  be  seen,  situated  between  two  of  the  four  beds  composing 


80 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


the  filter.  In  Fig.  42  is  shown  a  nearer  view  of  one  of  the  beds 
with  the  distributing  trough  and  its  branches  on  the  surface 
of  the  bed.  This  bed,  of  the  four  composing  the  filter,  was  not 
in  operation  at  the  time  the  photograph  was  taken. 

In  Fig.  38  is  shown  a  sand  filter  layout  with  three  beds. 
In  this  drawing  are  shown  the  sewer  leading  from  the  house,  the 
settling  tank,  the  siphon  chamber,  in  which  are  placed  two 
siphons,  the  effluent  sewers,  and  the  diverting  manhole,  from 


FIG.  40. — Portion  of  Distributing  Troughs  for  Sand  Filters. 

which  three  pipe  lines  convey  the  sewage  to  the  filter  beds. 
In  Fig.  39  is  shown  also  a  view  of  the  three  filter  beds,  one  of 
the  beds  being  shown  in  section.  Figs.  43  and  44  show  a  plan 
and  view  of  the  diverting  manhole. 

Where  sand  must  be  carted  in  to  form  the  filters,  the  embank- 
ments to  retain  the  sand  should  generally  be  formed  by  excavat- 
ing for  a  depth  of  two  feet  the  whole  area  upon  which  the  beds 
are  to  be  placed.  The  material  thus  excavated  will  usually 


SEWAGE    FILTERS 


81 


be  sufficient  to  form  the  embankments.  The  embankments 
should  usually  be  at  least  two  feet  wide  on  top  and  should  have 
side  slopes  of  one  and  a  half  to  one;  that  is,  the  bottom  width 
of  the  embankment  should  be  two  feet  plus  three  times  the 
height.  In  clay  soils  the  pits  for  the  filter  beds  may  be  excavated 
with  the  sides  vertical,  or  nearly  so.  The  bottom  of  each  bed, 


FIG.  41. 

as  it  is  prepared  for  the  placing  of  the  sand  which  is  to  compose 
the  filter,  should  slope  slightly  from  the  sides  toward  the  centre 
line  of  the  bed. 

Where  the  character  of  the  underlying  strata  of  soil  or  the 
presence  of  ground  water  requires  that  sand  niters,  whether 
natural  or  artificial,  should  be  underdrained,  this  may  be  accom- 
plished by  laying  a  longitudinal  main  drain  through  the  centre 

6 


82 


PRACTICAL    METHODS    OF    SEWAGE    DISPOSAL 


of  the  bed  at  a  depth  of  at  least  three  or  four  feet  below  the 
surface,  with  branches  each  way  at  intervals  of  about  fifteen  feet. 
The  main  underdrain  should  be  six  inches  in  diameter,  of  agri- 
cultural tile  or  of  vitrified  sewer  pipe,  laid  with  open  joints, 
and  should  have  a  fall  of  at  least  six  inches  per  hundred  feet. 
The  branches  may  be  of  three-inch  agricultural  tile. 


FIG.  42. 

In  large  installations  for  cities  and  villages  it  is  usual  to 
install  either  plural  alternating  siphons  or  apparatus  known 
as  sewage  feeds,  by  means  of  which  the  contents  of  the  dosing 
chamber  are  discharged  upon  the  different  beds  in  rotation, 
there  generally  being  four  or  five  beds  constructed  in  each  unit. 
This  requires  a  separate  siphon  or  sewage  feed  for  each  bed,  and 


SEWAGE   FILTERS 


83 


entails  considerable  expense.  However,  for  smaller  plants  such 
as  are  now  being  considered,  two  ordinary  siphons  may  be 
placed  in  the  same  dosing  chamber  as  described  in  Chapter  III, 
and  so  primed  as  to  discharge  alternately.  Then,  by  means 
of  a  diverting  manhole  or  chamber  through  which  the  dose  must 
pass,  the  effluent  may  be  diverted  onto  two  beds  in  rotation, 
allowing  a  third  bed  to  rest,  or,  if  there  are  five  beds,  it  may 
be  diverted  onto  two  pairs  of  beds  in  rotation,  allowing  a  fifth 


Stop  plank 


FIG.  43. — View  of  Diverting  Manhole. 

bed  to  rest.  For  instance,  in  the  case  of  five  beds,  a  diverting 
manhole  may  be  constructed  as  shown  in  Fig.  45,  and  arrange- 
ments may  be  made  to  couple  bed  No.  3  with  No.  2  or  No.  4, 
allowing  bed  No.  i  or  No.  5  to  rest  by  means  of  the  stop-plank 
to  cut  off  the  flow  to  either  of  these  beds,  as  shown  in  the  illus- 
tration. Then,  when  bed  No.  3  is  to  be  rested,  stop-planks  A 
and  B  are  both  closed,  and  the  stop-planks  against  all  pipe 
outlets  are  raised.  If  it  is  desired  to  throw  bed  No.  i  out  of 
use,  the  stop-plank  is  placed  against  the  end  of  the  pipe  lead- 


84 


PRACTICAL    METHODS    OF   SEWAGE    DISPOSAL 


ing  to  this  bed,  stop-plank  A  is  raised,  and  stop-plank  B  is 
lowered.  One  siphon  will  then  discharge  onto  beds  Nos.  4 
and  5,  and  with  the  next  filling  of  the  siphon  chamber  the 
second  siphon  will  discharge  onto  beds  Nos.  2  and  3.  By  a 
proper  combination  of  the  stop-plank  positions,  any  two  sets 
of  two  beds  each  may  receive  alternately  the  discharge  from 
the  siphon  chamber  while  the  remaining  single  bed  may  be  left 
resting.  The  method  for  operating  the  beds  in  rotation  described 
above  may,  of  course,  be  easily  applied  when  only  three  beds 


FIG.  44. — Plan  of  Diverting  Manhole. 

are  constructed.  A  provision  for  allowing  one  bed  to  be  thrown 
out  of  use  for  a  week  or  so  at  a  time  is  very  necessary  for  the 
reasons  stated  above. 

At  intervals  of  several  weeks  it  will  be  found  necessary  to 
break  up  the  surface  of  each  bed  by  raking  or  else  to  remove 
a  thin  coating  of  clogging  material.  This  should  be  done  after 
the  bed  has  been  rested  and  dried  out,  when  the  surface  matting 
may  be  taken  off  without  removing  much  sand.  To  provide 
for  operating  the  beds  in  winter,  in  the  late  fall,  before  the  ground 


SEWAGE    FILTERS 


85 


has  frozen,  ridges  and  furrows  should  be  formed  on  the  surface 
of  the  beds,  similar  to  those  shown  in  Fig.  51.  The  furrows 
should  be  two  or  three  feet  apart  and  eight  to  twelve  inches 
deep.  Then  when  effluent  is  discharged  onto  the  beds  in  freezing 
weather,  as  it  fills  the  furrows,  an  ice  roof  will  gradually  form, 
spanning  the  furrows  and  protecting  the  sides  and  bottoms 


TIG.  45. — Five-way  Diverting  Manhole. 

of  the  furrows  from  freezing,  especially  if  a  snowfall  occurs 
before  severe  weather  sets  in.  It  will  sometimes  be  found 
necessary,  especially  with  small  beds  that  are  well  underdrained, 
to  provide  board  coverings  for  the  furrows  to  take  the  place  of 
the  natural  ice  roofs. 

The  effluent  from  the  tank  should  be  discharged  in  such 


86          PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

quantities  as  to  flood  the  entire  bed  to  a  depth  of  from  one  to 
two  inches,  except  that  some  of  this  effluent  will  immediately 
begin  to  seep  into  the  bed. 

Respecting  the  quality  and  relative  fineness  of  sand  suitable 
for  sewage  filters,  it  should  be  noted  that  certain  empirical 
methods  of  measurement  have  been  developed  for  use  in  com- 
paring the  size  and  uniformity  of  particles  of  various  sands. 
These  measures  are  (i)  the  "effective  size,"  and  (2)  the  " uni- 
formity coefficient."  The  " effective  size"  is  the  size  of  sand 
particle  expressed  in  millimetres  compared  to  which  ten  per 
cent  by  weight  of  the  particles  in  the  sample  is  finer.  The 
"uniformity  coefficient"  is  the  ratio  of  the  size  of  grain  which 
has  sixty  per  cent  of  the  sample  finer  than  itself  to  the  size 
which  has  ten  per  cent  finer  than  itself. 

Concerning  the  grades  of  sand  through  which  sewage  may 
be  successfully  and  properly  treated  by  intermittent  filtration, 
it  has  been  found  that  the  "effective  size"  should  not  be  less 
than  .20  of  a  millimetre,  nor  greater  than  .50  of  a  millimetre, 
and  the  "uniformity  coefficient"  should  generally  be  from  1.5 
to  3.0,  when  sewage  is  applied  at  the  usual  rate.  If,  however, 
the  sand  is  clean  and  sharp,  but  has  an  "effective  size"  some- 
what smaller  than  the  limit  above  stated,  it  may  sometimes 
be  found  suitable. 

In  the  case  of  any  sewage-disposal  project  of  considerable 
magnitude,  where  any  doubt  exists  as  to  the  suitability  of  the 
sand  available  for  use  in  sand  filters,  analyses  of  representative 
samples  of  the  sand  should  be  arranged  for,  and  competent 
engineering  advice  should  be  sought  before  any  large  outlay  is 
incurred.  In  general,  however,  it  may  be  said  that  any  clean, 
sharp  sand  suitable  for  building  use  is  suitable  for  sand-filter 
beds  in  any  situation.  Obviously,  the  coarseness  of  the  sand 
plays  no  part  in  its  suitability  as  a  filtering  medium  if  the  sand 


SEWAGE   FILTERS  87 

occurs  in  a  natural  bed  and  underdrains  are  not  necessary, 
since  no  question  of  the  discharging  of  an  unpurified  effluent 
would  ordinarily  arise  in  such  cases.  < 

CONTACT  BEDS 

The  treatment  of  sewage  in  contact  beds  consists  in  dis- 
tributing the  effluent  from  settling  tanks  over  beds  of  broken 
stone,  furnace  slag,  or  other  similar  material  contained  in 
water-tight  compartments  and  allowing  the  beds  to  fill  so  that 
the  spaces  between  the  filtering  material  will  be  filled  with 
the  sewage  effluent.  These  beds  are  so  arranged  that  the  effluent 
is  held  in  contact  with  the  filtering  material  for  a  fixed  interval 
of  time  and  then,  usually  by  means  of  special  siphons  called 
"  timed  siphons,"  or  other  automatic  devices,  it  is  discharged 
from  the  beds  onto  sand  filters  for  further  treatment,  or  into 
streams,  as  the  case  may  be. 

The  process  involves,  as  in  intermittent  sand  filtration, 
the  nitrifying  or  oxidizing  agencies  of  bacterial  action,  and 
differs  from  intermittent  filtration  and  from  treatment  of  sewage 
on  sprinkling  filters  principally  in  the  fact  that  the  flow  of 
effluent  through  the  beds  is  arrested  and  the  liquid  sewage  held 
in  contact  with  the  filtering  material,  as  noted  above. 

Much  smaller  areas  of  filter  beds  are  required  than  in  the 
case  of  sand  filters,  and  for  this  reason  this  form  of  filter  will 
often  be  found  preferable.  The  conditions  which  result  in  its 
selection  are  usually  either  the  unsuitable  character  of  the  soil 
or  the  presence  of  ground  water,  making  the  installation  of  sub- 
surface irrigation  systems  impracticable;  or  the  absence  of  sand 
deposits  or  the  high  cost  in  any  locality  of  sand  suitable  for 
sand-filtration  beds,  making  their  construction  difficult  or 
expensive. 


88         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

The  walls  and  floor  of  a  contact  bed  are  generally  constructed 
of  concrete,  and  the  filter  should  be  rectangular  in  form,  as  it 
is  easier  to  distribute  the  effluent  uniformly  over  a  bed  of  this 
shape.  The  details  given  in  Chapter  II  for  constructing  the 
walls  and  floors  of  settling  tanks  will  serve  as  a  general  guide 
in  the  construction  of  contact  beds. 

The  real  work  of  the  contact  filter  is  carried  on  during  the 
period  of  "  res  ting  empty,"  that  is,  after  the  effluent  has  been 
withdrawn  from  the  bed.  While  the  effluent  fills  the  beds,  much 
of  the  suspended  solid  matter,  together  with  a  large  proportion 
of  the  bacteria  contained  in  the  sewage,  adheres  to  a  gelatinous 
film  which  has  formed  on  the  surfaces  of  the  stones  or  other 
materials  forming  the  beds.  This  interval  of  "resting  full" 
should  usually  be  about  two  hours.  Then,  when  the  liquid 
portion  is  withdrawn  from  the  bed,  air  is  drawn  in  between  the 
stones,  enabling  the  nitrifying  or  aerobic  bacteria  to  do  their 
work  of  breaking  down  both  the  suspended  and  the  partially 
dissolved  organic  matters  which  have  been  contained  in  the 
sewage  and  which  have  adhered  to  the  filter  material.  It  is 
believed,  that  some  oxidation  of  that  portion  of  the  organic 
matter  which  is  in  true  solution  is  also  accomplished  when 
the  effluent  passes  over  the  gelatinous  covering  of  the 
stones  by  reason  of  the  oxygen  which  has  been  absorbed  by 
this  covering. 

The  interval  when  the  bed  is  "  res  ting  empty"  should  be  con- 
siderably longer  than  the  combined  intervals  when  the  bed  is 
filling,  "  resting  full,"  and  emptying.  For  this  reason  there 
should  be  a  series  of  from  three  to  five  beds  in  order  that  it 
will  not  be  necessary  to  turn  the  effluent  from  the  settling  tank 
continuously  onto  one  bed,  which  would  result  in  the  clogging 
of  this  bed  with  suspended  matters.  The  additional  third  (or 
fifth)  bed  also  gives  opportunity  for  allowing  each  bed  in  turn 


House 


PROFILE 


PLAN   OF   SEWAGE   DISPOSAL  WORKS 

FOR 

MR.CHARLES   L.A.WHITNEY 

ALBANY,  N.Y. 


/ 

2"riank  Baffles 
Tank 

1 

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Dosing  Cham. 

c-: 

rf 

I'xio' 

A 

2"  Plank  Baffles 

Tank 
4'6"x  9' 

| 

T 

Two  5  Siphons 

f  _~ 

SETTLING  TANKS 


SCALE  OP  FEET 
5  1 


PLAN 


.,-.•••. m.  oa.ov^ r%?<r.& 

-.^-   -<.cv;^:v;   ...sv.v--  ^,\\--  ^    .....,- ^-,,.-^   .--;-;•.-•-•- 


LONGITUI 


NOTES 

Walls  of  Tanks  and  Contact  Beds  to  be  of  Concrete. 
Tanks  and  Dosing  Cham,  to  have  2  "  PI.  covers. 
Contact  Beds  to  be  filled  to  Flow  Line  with  ^ stone. 
Distributing  pipes  in  Contact  Beds  to  be  graded  by 
•xperiment  to  regulate  flow. 


tct  Beds 


Horseshoe     ^    Tile.        Underdrains 


EL90.8* 


Flow  Line 


EL90.34 


$£•:  ;.'£  |     ^  |          J J-^*«"'*"*  _^_ 

: 


^pv*f& 


1  SECTION 


HERSCHEL  ROBERTS  Civil  Engineer 
Albany,  N.Y. 


46 


SEWAGE   FILTERS  89 

to  be  thrown  out  of  use  for  intervals  of  a  week  or  so  at  a  time, 
which  is  also  necessary  to  keep  the  beds  up  to  their  proper 
efficiency  and  obviate  the  necessity  of  cleaning  or  renewing  the 
filter  material  oftener  than  once  in  seven  or  eight  years. 

In  Fig.  46  is  shown  in  plan  and  section  a  sewage-disposal 
plant  for  the  residence  of  Mr.  Charles  L.  A.  Whitney,  of  Albany, 
N.  Y.,  consisting  of  a  settling  tank,  dosing  chamber,  and  con- 
tact beds.  This  plant  is  designed  to  serve  twenty-five  persons, 
although  the  settling  tanks  have  a  capacity  for  double  the 
amount  of  sewage  on  the  usual  basis  of  design. 

The  depth  of  filtering  material  in  the  beds  should  preferably 
be  four  or  five  feet,  although,  where  operating  head  or  fall  is 
limited,  this  depth  may  be  decreased  to  three  feet.  The  floor 
of  the  bed  should  slope  toward  the  outlet  end  at  a  rate  of  about 
one-eighth  of  an  inch  per  foot. 

Various  materials  are  used  to  form  the  body  of  the  filter, 
such  as  broken  stone,  coke,  broken  brick,  and  furnace  slag, 
but  the  material  used  should  not  be  such  as  will  disintegrate 
readily,  and  for  this  reason  broken  limestone,  from  one-half 
inch  to  one  and  one-half  inches  in  size,  with  perhaps  two-inch 
stones  for  the  bottom  six  inches  of  the  bed  surrounding  the 
underdrains,  is  most  suitable  for  small  plants. 

These  underdrains  should  be  constructed  of  horse-shoe 
tiling,  and  in  the  case  of  beds  more  than  eight  or  ten  feet  wide 
should  preferably  be  laid  with  short  branches  reaching  from  a 
main  drain  laid  along  the  centre  of  the  floor  of  the  bed; 
or  these  drains  may  be  laid  in  parallel  lines,  as  shown  in 
Fig.  46. 

In  order  to  alternate  the  discharge  of  effluent  from  the 
settling  tank  onto  different  beds  in  turn  and  to  provide  for  more 
uniformly  distributing  the  effluent  over  all  portions  of  the  bed, 
the  settling-tank  effluent  should  be  collected  as  in  the  other 


90          PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

methods  of  disposal  described,  in  a  siphon  or  dosing  chamber, 
from  which,  by  means  of  alternating  siphons,  it  may  be  delivered 
to  the  proper  bed. 

In  the  case  of  a  group  of  three  beds  or  five  beds,  diverting 
chambers  with  stop-planks,  similar  to  those  described  in  con- 
nection with  intermittent  sand  filters,  may  be  provided  to  allow 
the  throwing  out  of  use  of  each  of  the  beds  in  turn  for  a  week 
or  so  at  a  time.  In  the  smaller  plants  accommodating  up  to 
one  hundred  and  fifty  persons,  it  is  hardly  necessary  to  provide 
for  more  than  three  beds,  thus  allowing  opportunity  for  each 
one  to  rest  for  one  week  in  every  three  to  six  weeks,  which  will 
result  in  a  temporary  increase  of  fifty  per  cent  in  the  rate  of 
application  of  effluent  to  the  remaining  beds.  In  the  case 
of  the  larger  plants,  especially  if  they  are  to  be  operated  con- 
tinuously, it  is  better  to  construct  five  beds  so  that  two  pairs 
of  two  beds  each  may  be  used  alternately,  leaving  one  bed,  or 
twenty  per  cent  of  the  total  area,  out  of  use.  This  will  re- 
sult in  an  increase  of  but  twenty-five  per  cent  in  the  rate  of 
application  of  effluent  to  the  four  beds  in  use. 

With  the  usual  rates  of  operation  for  contact  beds,  one  filling 
per  day  of  the  beds  will  result,  and,  if  the  dosing  of  the  beds  is 
carried  on  as  above  and  as  described  in  the  portion  of  this 
chapter  dealing  with  the  dosing  of  intermittent  sand  filters, 
but  two  siphons  in  the  dosing  tank,  constituting  double  alter- 
nating siphons,  will  be  necessary.  Such  an  arrangement  will 
eliminate  the  necessity  of  installing  plural  alternating  siphons 
consisting  of  three  or  more  siphons,  the  cost  of  which  is  not 
warranted  in  connection  with  small  plants,  since  the  double 
alternating  siphons  will  insure  proper  operation  of  the  beds  at 
much  less  cost.  Of  course,  in  the  larger  plants  where  two  beds 
are  dosed  at  each  discharge  of  a  siphon,  a  larger  siphon  chamber 
is  necessary  with  the  two  siphons,  but  the  extra  cost  of  a  larger 


SEWAGE   FILTERS  91 

siphon  chamber  would  in  most  cases  be  more  than  offset  by 
the  increased  cost  of  plural  alternating  siphons. 

The  main  effluent  carrier  from  the  siphon  chamber  to  each 
contact  bed  should  discharge  into  a  half-tile  carrier,  with 
branches,  laid  on  the  surface  of  the  contact  bed,  as  shown  in 
Fig.  46. 

Each  contact  bed  should  be  provided  at  the  outlet  end  with 
a  " timed"  siphon  set  in  a  separate  chamber  of  two  compart- 
ments, as  shown  in  the  drawing.  The  diameter  of  the  timed 
siphons  should  generally  be  that  of  the  next  larger  size  than  that 
indicated  for  the  dosing-chamber  siphons.  As  shown  in  the 
illustration,  where  only  three  beds  are  necessary,  the  third  timed 
siphon  may  be  dispensed  with  if  arrangements  are  made  to 
permit  the  use  of  one  siphon  for  discharging  either  the  middle 
or  the  outside  bed  on  that  side,  and  to  permit  the  use  of  the 
other  siphon  for  discharging  either  the  middle  bed  or  the  bed 
on  the  other  side.  In  such  installations  gates  or  valves  must 
be  placed  on  the  outlets  of  the  contact  beds  to  prevent  the  filling 
of  the  bed  that  is  out  of  use  by  back  flow  from  the  timed  siphon 
chamber  used  to  discharge  the  adjacent  bed. 

The  cost  of  contact  beds  is  considerably  greater  than  the 
cost  of  intermittent  sand  filters,  especially  when  sand  of  proper 
quality  is  available,  but  their  construction  is  advised  in  many 
cases  where  sub-surface  irrigation  is  not  feasible,  where  the 
premises  are  subject  to  overflow  or  the  ground-water  level  is 
high,  and  where  it  is  not  practicable  to  construct  sand  filters. 

In  the  following  table  are  given  the  proper  number  of  units 
or  beds  for  contact  filters  of  different-sized  installations,  together 
with  the  required  area  of  each  filter,  the  depth  of  the  filter 
medium  in  all  beds  being  four  feet.  The  table  also  shows  the 
dimensions  of  the  siphon  chamber  adjacent  to  the  settling  tank 
and  the  diameter  of  the  siphons  necessary  to  discharge  the 


92 


PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


effluent  in  proper  volumes  onto  each  contact  bed,  or  each  pair 
of  contact  beds.  Where  it  is  necessary  to  decrease  the  depth 
of  the  contact  beds  to  three  and  one-half  or  three  feet,  owing 
to  lack  of  operating  head  or  fall,  a  proportionate  increase  should 
be  made  in  the  area  of  each  bed. 

TABLE  V 
FOR.  USE  IN  CONSTRUCTING  CONTACT  BEDS 


Persons 
Served  by 
Sewer. 

No.  of 
Beds. 

Area  of  Each 
Bed 
(Square  Feet)  . 

Mean  Width 
and  Length 
of  Siphon 
Chamber 
(Feet). 

Diameter 
of 
Siphons 
(Inches). 

Distance  from 
Roof  of  Settling 
Tank  to  Top  of 
Wall  between 
Settling  Tank  and 
Siphon  Chamber 
(Inches). 

4 

3 

2O 

3     x   4.5 

5 

12 

8 

3 

40 

4     x   6.5 

5 

12 

12 

3 

60 

6     x    7 

5 

12 

15 

3 

70 

6x8 

5 

12 

25 

3 

IOO 

6x8 

6 

16 

35 

3 

130 

7x9 

6 

16 

50 

3 

1  80 

8.5x10 

6 

16 

75 

3 

280 

10       X  II 

8 

18 

IOO 

3 

370 

12       X  12 

8 

18 

125 

3 

460 

12       XI4 

8 

20 

150 

3 

550 

12     xi6.5 

8 

2O 

175 

5 

390 

13     xi4 

10 

2O 

200 

5 

440 

14     xis 

10 

2O 

250 

5 

550 

15     xi8 

10 

20 

300 

5 

660 

17     xi9 

10 

2O 

350 

5 

770 

18       X2I 

IO 

2O 

400 

5 

880 

18     x24 

IO 

20 

450 

5 

990 

20       X2I 

12 

20 

500 

5 

IIIO 

20       X23 

12 

20 

In  the  above  table,  as  in  the  previous  tables,  in  indicating 
the  height  to  which  the  dividing  wall  between  the  settling  tank 
and  siphon  chamber  should  be  carried,  allowance  is  made  for  a 
draught  upon  the  contents  of  the  settling  tank  at  each  discharge 
of  a  siphon  of  from  four  to  eight  inches.  In  the  discussion 
relating  to  siphon  chambers  in  connection  with  the  description 
of  intermittent  sand  filters  will  be  found  the  necessary  details  as 
to  the  discharging  depths  of  siphons  of  different  diameters  and 


SEWAGE   FILTERS  93 

the  necessary  depths  of  the  siphon  chambers  in  which  such 
siphons  are  to  be  placed.  The  construction  of  contact  beds  will 
naturally  be  approached  with  hesitancy  by  property  owners 
and  others  not  familiar  with  such  work,  and  it  is  strongly  recom- 
mended that  where  it  is  possible  the  services  of  a  sanitary 
engineer  be  engaged  to  design  and  supervise  the  construction 
of  a  plant  involving  any  considerable  outlay,  unless  it  is  felt 
that  the  descriptions  and  directions  given  above  have  afforded 
a  clear  understanding  of  the  design  and  construction  of  this 
type  of  sewage-disposal  works. 

SPRINKLING  FILTERS 

One  of  the  more  recently  developed  methods  of  sewage 
disposal, — the  sprinkling-  or  trickling-filter  system, — has  for 
its  principal  feature  the  thorough  aeration  of  the  settling-tank 
effluent  before  its  passage  through  the  filter.  This  filter,  like 
the  contact  filter,  is  of  the  rapid,  coarse-grained  type,  but  in 
its  operation  resembles  the  process  of  intermittent  sand  filtra- 
tion in  that  the  sewage  effluent  passes  through  the  filter  con- 
tinuously without  being  held  in  contact  with  the  filtering 
material  as  in  the  contact  bed.  The  aeration  of  the  sewage 
effluent,  which  very  greatly  aids  the  final  process  of  nitrification 
or  oxidation  in  the  filter,  is  accomplished  by  spraying  the  sewage 
effluent  over  the  surface  of  the  beds  through  a  series  of  riser 
pipes  with  nozzles,  or  allowing  it  to  fall  in  fine  streams  on  dash 
plates  which  cause  it  to  sprinkle  over  the  beds  and  thus  to 
absorb  oxygen  from  the  air. 

Sprinkling  filters  produce  an  effluent  with  a  considerably 
less  degree  of  purification  than  sand  filters,  but  may  in  general 
be  said  to  produce  a  more  stable  effluent,  that  is,  one  less  liable 
to  subsequent  putrefaction  than  the  effluent  from  contact  beds. 


94         PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

Furthermore,  with  the  usual  depths  of  contact  beds  and  sprin- 
kling niters,  an  area  approximately  four  times  greater  is  required 
to  treat  the  same  amount  of  sewage  on  contact  beds  than  is 
necessary  if  sprinkling  niters  are  constructed.  However,  since 
the  effluent  from  sprinkling  filters  is  much  more  turbid,  neces- 
sitating, in  most  cases,  subsequent  sedimentation  before  dis- 
charge; since  considerably  greater  operating  head  or  fall  is 
necessary;  and  since  their  operation  requires  much  more  super- 
vision, the  construction  of  sprinkling  niters  is  not  generally 
as  advisable  as  contact  beds  for  small  installations,  especially 
in  cold  climates. 

The  construction  of  sprinkling  filters  as  compared  to  contact 
filters  differs  principally  in  the  size  and  depth  of  filtering  material, 
in  the  means  provided  for  distributing  the  effluent  over  the 
beds,  and  in  the  arrangements  for  draining  the  filter. 

The  depth  of  filtering  material  in  a  sprinkling  filter  is  usually 
from  five  to  ten  feet,  preferably  not  less  than  eight  feet.  The 
material  for  the  filter  is  the  same  as  that  used  for  contact  filters 
but  the  fragments  should  be  from  one  to  three  inches  in  diameter. 
Instead  of  a  system  of  tile  underdrains  on  the  floor  of  the  filter, 
a  false  floor  of  perforated  tile,  rectangular  in  section,  or  of  half 
tile,  circular  in  section,  with  drainage  holes  cut  out  along  the 
sides,  should  be  laid  over  the  entire  floor  of  the  filter.  As  the 
settling-tank  effluent  is  sprayed  on  the  filter  it  passes  down- 
ward between  the  spaces  of  the  filtering  material,  and  reaching 
the  floor  of  the  filter  is  collected  in  a  main  drainage  channel, 
through  which  it  passes  to  the  outfall  sewer,  and  thence  to  the 
final  settling  tank  or  into  the  stream. 

As  with  contact  beds  and  sand  niters,  intermittency  of 
application  of  the  effluent  to  the  filter  is  essential  for  proper 
action  of  the  filter,  and  this  is  accomplished  as  in  the  other 
types  of  filters  by  means  of  automatic  siphons  placed  in  dosing 


SEWAGE    FILTERS 


95 


tanks.  These  tanks,  however,  are  of  special  design  in  the  case 
of  sprinkling  niters.  Each  siphon  discharges  into  a  main  carrier 
of  iron  pipe  which  extends  sometimes  over  the  surface  of  the 
filter,  but  generally  along  the  floor  of  the  filter.  The  main  car- 
rier has  branch  pipes  of  smaller  diameter  extending  at  right  angles 
nearly  to  the  sides  of  the  filter.  On  these  branches  vertical 
riser  pipes  spaced  about  ten  feet  apart  are  connected,  and  these 
riser  pipes  extend  a  few  inches  above  the  surface  of  the  filter. 
Nozzles  are  fitted  to  the  ends  of  the  riser  pipes  by  means  of 


FIG.  47. — View  of  Sprinkling  Filter  at  Danville,  Pa.,  in  Winter. 

which  the  sewage  effluent,  under  pressure,  is  sprinkled,  at  short 
intervals,  in  the  form  of  a  fine,  umbrella-shaped  spray,  over  the 
surface  of  the  filter.  This  results  in  a  thorough  aeration  of  the 
effluent  before  it  reaches  the  filtering  material,  and  makes  this 
form  of  filter  very  effective. 

In  Fig.  47  is  shown  a  view  of  a  sprinkling  filter  at  Danville, 
Pa.,  operating  when  the  temperature  was  14°  below  zero.  It  is 
generally  believed,  however,  that  in  cold  climates  it  is  advisable 
to  house  small  sprinkling  filters. 


96          PRACTICAL    METHODS    OF    SEWAGE    DISPOSAL 

Owing  to  the  rather  complicated  hydraulic  features  and  the 
somewhat  difficult  engineering  principles  involved  in  the  con- 
struction and  operation  of  sprinkling  or  trickling  filters,  it  is 
not  deemed  advisable  to  attempt  to  describe  them  in  sufficient 
detail  to  furnish  directions  for  their  construction.  The  design 
of  a  sprinkling-filter  system  for  small  as  well  as  for  large  installa- 
tions should  always  be  entrusted  to  an  engineer  conversant 
with  this  line  of  sanitary  engineering.  It  is  believed,  however, 
that  the  description  of  such  niters  given  above  will  aid  those 
who  are  about  to  install  sewage-disposal  plants  in  the  selection 
of  the  type  of  plant  best  suited  to  their  particular  needs  and 
conforming  to  the  conditions  peculiar  to  their  situation. 

Summarizing  the  foregoing  descriptions  and  directions  with 
reference  to  sewage  filters,  it  may  be  stated  that  where  natural 
facilities  for  disposing  of  sewage  by  simpler  methods  do  not 
exist,  the  construction  of  a  sewage  filter  of  some  one  of  the 
above  described  types  offers  a  solution  of  every  problem  thus 
encountered.  It  is  well  to  repeat  that  sub-surface  irrigation, 
where  feasible,  should  be  adopted,  and  this  will  be  the  method 
indicated  in  a  large  majority  of  cases  where  small  disposal 
plants  are  to  be  constructed. 

The  principal  point  to  be  remembered  in  connection  with 
sewage  filters  is  that  their  construction  is  but  a  good  beginning, 
and  that  their  proper  operation  is  very  necessary  to  the  success 
of  the  undertaking.  They  constitute,  with  the  developed 
bacteria  in  the  filter,  a  rather  sensitive  mechanism  capable  of 
efficient  work  if  properly  handled,  but  each  filter  unit  must 
be  carefully  operated  and  must  be  regularly  given  extended 
periods  of  rest  for  the  restoration  of  the  void  or  open-space 
capacity  of  the  filter,  and  to  provide  for  the  necessary  aeration 
of  the  filtering  material. 

The  peculiar  action  which  takes  place  in  a  filter  in  the  reduc- 


SEWAGE   FILTERS  97 

tion  of  sewage,  and  which  is  not  even  yet  fully  known,  is  best 
evidenced  by  the  fact  that  sewage  niters,  especially  of  the 
coarse-grained  type,  do  not  attain  their  highest  efficiency  until 
after  several  weeks  or  months  of  operation. 

With  a  knowledge  of  these  points,  it  will  be  seen  that  there 
should  be  little  divergence  from  accepted  standards  in  the 
construction  and  operation  of  sewage  niters  if  they  are  to  prove 
satisfactory  when  installed. 

7 


CHAPTER  VI 
BROAD   IRRIGATION 

For  many  years  it  has  seemed  to  thoughtful  persons  that 
permitting  sewage,  either  from  single  houses  or  from  larger 
communities,  to  be  turned  into  streams  was  a  mistaken  policy 
because  of  the  waste  of  manurial  elements  involved.  It  has  long 
been  understood  that,  in  order  to  maintain  the  fertility  of  the 
soil,  a  constant  application  of  fertilizers  was  necessary,  and, 
while  undoubtedly  many  farms  are  managed  without  any  such 
repeated  applications,  the  more  scientific  and  modern  farmer 
believes  to-day  that  the  frequent  and  abundant  use  of  fertilizer 
is  the  foundation  of  his  success. 

In  ordinary  sewage  there  exists  a  certain  amount  of  fertilizing 
elements.  Two  prominent  English  chemists,  not  many  years 
ago,  proved  by  their  analyses  that  in  ordinary  sewage  there 
existed  the  essential  elements  of  a  good  fertilizer  to  the  value  of 
$2  per  year  for  each  person  contributing  to  that  sewage. 
Other  chemists,  working  at  the  problem  in  other  ways,  have 
reached  about  the  same  result,  and  there  can  be  little  doubt 
of  their  accuracy  if  the  fertilizing  elements  alone  are  considered. 
In  applying  these  figures  to  the  sewage  of  a  city  the  difficulty 
has  always  been  that  the  fertilizing  elements  have  been  so 
thoroughly  covered  up  with  the  large  volume  of  water  present 
in  the  sewage  that  it  has  been  practically  impossible  to  separate 
them  from  the  water.  Thus,  in  a  city  of  100,000  persons,  the 
fertilizer  in  the  sewage  might,  indeed,  be  worth  $200,000,  but 
to  realize  this  amount  it  must  be  separated  from  the  10,000,000 
gallons  of  water — a  task  which  is  so  tremendous,  if  not  impos- 
sible, as  to  make  the  value  of  the  fertilizer  of  no  account.  In 

98 


BROAD   IRRIGATION  99 

those  parts  of  the  country  where  the  water  itself  has  a  value, 
as  in  the  irrigated  lands  of  the  West,  the  fertilizing  elements 
of  the  sewage  would  be  added  to  the  value  of  the  water,  so  that 
sewage  used  for  irrigation  would  be  worth  not  merely  the  value 
of  the  water  alone,  but  also  the  value  of  the  fertilizer  present 
in  that  water. 

Another  difficulty  in  making  use  of  the  combined  water  and 
fertilizer  is  that  the  large  amount  of  water  involves  a  large  area 
of  land  and  suitable  soil,  on  which  irrigation  may  be  practised, 
in  the  immediate  vicinity  of  the  city.  This  combination  of 
agricultural  soil  of  suitable  texture  at  a  suitable  price  for  farming 
operations  is  so  seldom  found  that  this  in  itself  usually  pre- 
cludes any  application  of  the  use  of  sewage  for  irrigation. 

In  the  case  of  the  sewage  from  a  single  house,  however, 
the  possibility  of  making  use  both  of  the  water  and  the  fertilizer 
in  sewage  is  not  so  difficult.  Recent  writers  on  irrigation  have 
pointed  out  that,  while  irrigation  of  late  years  has  made  most 
headway  in  the  semi-arid  districts  of  the  West,  there  are  many 
opportunities  for  its  successful  and  profitable  utilization  in  the 
East,  and  Mr.  Lute  Wilcox,  in  a  recent  book  on  irrigation,  says: 
"The  farmer  who  has  a  soil  containing  an  abundance  of  all  the 
needed  elements  in  a  proper  state  of  fineness  cannot  but  deem 
himself  happy  if  he  have  always  ready  at  hand  the  means  of 
readily  and  cheaply  supplying  all  the  water  needed  by  his  soil 
and  growing  crops,  just  when  and  in  just  such  quantities  as  are 
needed.  Happier  still  may  he  be  when  he  realizes  that  he  need 
have  no  'off  years,'  and  he  knows  that  the  waters  he  admits 
to  his  fields  at  will  are  freighted  with  rich  fertilizing  elements 
usually  far  more  valuable  to  the  growing  crops  than  any  that 
he  can  purchase  and  apply  at  a  costly  rate — a  cost  that  makes 
serious  inroads  upon  the  profits  of  the  majority  of  farmers 
cultivating  the  worn-out  or  deteriorated  soils  in  the  older  States 


100        PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

year  by  year.  Fertilizers  are  already  needed  for  the  most 
profitable  culture  on  many  farms  in  Iowa,  Minnesota,  Eastern 
Kansas,  and  Nebraska,  in  Missouri,  and  in  all  States  east  of 
those  named." 

Perhaps  the  greatest  uncertainty  in  the  matter  of  farming 
is  the  available  water  coming  from  the  clouds.  In  one  year 
the  rainfall  may  come  at  the  proper  time  to  moisten  the  seed 
and  to  insure  a  rapid  germination.  These  early  rains  may  be 
followed  by  showers  at  proper  intervals  to  supply  the  little 
rootlets  with  the  necessary  moisture  so  that  the  growth  of  the 
plant  may  be  constant  and  vigorous.  During  the  ripening 
season  the  rains  may  be  withheld  so  that  the  harvest  is  insured 
under  the  most  favorable  conditions.  In  other  years,  however, 
the  spring  rains  may  be  so  continuous  as  to  cause  the  seeds 
to  rot,  requiring  a  second  sowing.  Then  the  rains  may  fail  so 
that  the  seeds  either  fail  to  germinate,  or  at  best  produce  scat- 
tered and  imperfect  growths.  At  the  time  of  harvest  storm 
may  follow  storm,  so  that  the  harvesting  of  those  plants  which 
have  developed  is  made  almost  impossible. 

Irrigation  tends  in  part  to  correct  these  difficulties,  since  it 
furnishes  the  soil  with  the  needed  water  at  times  when  the  lack 
of  rain  would  cause  an  entire  failure  in  future  growth.  Irriga- 
tion, of  course,  cannot  prevent  rainfall,  and  it  may  be  that 
after  a  copious  soaking  of  the  ground  with  the  irrigating  water 
a  heavy  rain  may  follow,  resulting  in  an  excess  of  moisture  as 
bad  for  the  ground  as  none  at  all.  The  possibility  of  irrigation 
cannot  prevent  excessive  rains  at  the  time  of  harvest,  but  the 
advantages  of  being  able  to  control  the  soil  moisture  during  the 
period  of  growth  are  more  than  enough  to  counterbalance  any 
possible  disadvantages.  During  the  summer  months  evapora- 
tion is  very  high,  the  dryness  of  the  air  and  the  high  temperature 
combining  to  draw  moisture  from  the  soil  in  considerable  quan- 


BROAD   IRRIGATION      V //•  *>" 

tity.  Then,  too,  the  plants  themselves,  while  absorbing  moisture 
from  their  roots,  evaporate  moisture  through  their  leaves, 
and  agricultural  stations  have  made  extensive  studies  on  the 
amount  of  this  evaporation  from  different  plants.  The  teaching 
of  it  all  is  that  the  amount  of  water  which  can  be  utilized  by 
the  soil,  not  merely  for  the  sake  of  the  growth  of  the  plants 
themselves,  but  to  make  up  for  the  demands  of  evaporation, 
is  very  high. 

Mr.  Newell,  of  the  United  States  Geological  Survey,  points 
out  that  while  the  amount  of  water  required  for  raising  crops 
varies  according  to  soil  and  other  conditions,  yet  a  large  quantity 
is  required  to  maintain  the  soil  in  such  a  degree  of  saturation 
as  to  best  promote  the  vitality  of  the  plant  life.  He  shows  that 
for  each  ton  of  hay  raised  upon  an  acre,  from  three  hundred  to 
five  hundred  tons  of  water  must  be  furnished  either  by  rainfall 
or  by  artificial  means.  In  other  words,  since  water  covering 
an  acre  to  a  depth  of  one  inch  weighs  about  one  hundred  and 
thirteen  tons,  it  would  be  necessary  to  cover  an  acre  to  a  depth 
of  from  three  to  five  inches  if  that  acre  produced  one  ton  of  hay. 
From  actual  conditions,  he  shows  that  it  has  been  necessary, 
in  order  to  produce  five  tons  of  barley  hay  per  acre,  to  provide 
an  amount  of  water  which  would  cover  the  acre  to  a  depth  of 
twenty  inches.  Although  his  figures  have  special  reference  to 
the  semi-arid  regions  of  the  West  they  furnish  a  guide  for  the 
amount  of  water  which  may  profitably  be  used  in  addition  to 
the  rainfall,  which,  in  the  summer  months,  may  be  practically 
nothing  even  in  the  East.  From  three  to  six  inches  in  depth 
each  month  is  his  estimate  of  the  needed  water  for  successful 
crop  growing,  the  difference  depending  upon  the  character  of 
the  soil,  more  being  required  in  sandy  soils  and  less  where  the 
texture  is  finer. 

The  sewage  from  an  ordinary  household,  on  the  basis  of 


:10iJ       .PRACriCAL   METHODS   OF   SEWAGE   DISPOSAL 

30  gallons  per  head  per  day,  amounts  to  180  gallons  per  day,  or 
•about  5,400  gallons  per  month,  or  720  cubic  feet.  This  amount 
of  water  would  cover  an  acre  of  ground  to  a  depth  of  a  little  less 
than  one-fourth  of  an  inch,  and  it  is  plain  that  in  order  to  have 
the  sewage  of  a  single  house  furnish  the  necessary  amount  of 
water  for  successful  crop  growing,  the  area  required  is  only 
about  one-twelfth  of  an  acre,  or  an  area  about  60  feet  square. 

In  the  early  days  of  the  English  experiments  with  the  dis- 
posal of  sewage,  great  stress  was  laid  on  the  value  of  the  manurial 
elements  in  sewage,  and  many  tests  were  made  as  to  the  capacity 
of  various  soils  for  absorbing  the  moisture  present  in  sewage. 
One  of  the  most  enthusiastic  advocates  of  this  method  of  dis- 
posing of  sewage  was  Mr.  J.  Bailey  Denton,  who  was  able  to 
.act  as  engineer  for  many  installations  of  various  sorts.  As  a 
result  of  his  experience  he  came  to  the  conclusion  that  while 
the  area  depended  upon  the  character  of  the  soil,  and  while 
with  the  most  suitable  soil  a  very  large  amount  of  water  might 
be  taken  care  of,  under  ordinary  conditions  it  was  safest  to  so 
design  the  works  that  no  possibility  of  overloading  the  soil 
with  water  could  exist.  He  places  the  limits  of  population, 
the  sewage  from  whom  would  be  cared  for  on  an  acre,  between 
1,000  persons  per  acre  and  100  persons  per  acre.  More  recent 
experience,  together  with  constant  observation  of  farms  estab- 
lished in  the  early  period  of  the  practice,  indicates  that  the 
higher  value  is  too  great,  and  that  where  agricultural  processes 
alone  are  considered,  100  persons  per  acre  is  a  suitable  maximum 
value  for  irrigation  on  sandy  loam,  and  that  40  persons  per 
acre  is  a  suitable  number  where  the  soil  is  inclined  toward 
density  and  fine  texture.  Six  persons  in  a  household  would, 
according  to  Mr.  Denton,  require  from  one-seventh  to  one- 
seventeenth  of  an  acre.  The  amount,  indicated  by  the  com- 
putations made  earlier,  indicated  one-twelfth  of  an  acre  for 


BROAD   IRRIGATION 


103 


the  same  number  of  persons.  The  practical  agreement  of  the 
two  methods  of  computing  the  area  necessary  thus  makes  it 
possible  to  determine  in  either  way  the  amount  of  land  needed 
on  a  given  farm  for  disposing  of  the  household  sewage. 

The  effect  of  sewage  irrigation  has  been  found  to  be  most 
astonishing  so  far  as  the  increased  yield  of  the  soil  goes.  Some 
years  ago,  in  order  to  determine  just  the  effect  of  the  addition 
of  sewage  to  ordinary  farm  land,  a  certain  field  of  five  acres 
was  divided  into  four  equal  parts.  The  four  fields  were  treated 
as  follows:  Field  No.  i  received  no  sewage.  Field  No.  2  received 
six  inches  of  sewage  over  its  entire  area  on  each  of  five  successive 
months.  Field  No.  3  received  twelve  inches  of  sewage  on  each 
of  five  successive  months.  Field  No.  4  received  eighteen  inches 
of  sewage  on  each  of  five  successive  months.  The  following 
table  shows  the  results  of  three  successive  years'  experiments 
at  the  sewage  farm  referred  to  at  Rugby,  England,  the  figures 
being  the  number  of  pounds  of  green  grass  cut  from  the  fields. 

FIVE-ACRE   FIELD 


WITHOUT  SEWAGE. 

WITH  SEWAGE. 

Lot  i. 

Lot  2. 

Lot  3. 

Lot  4. 

20,814 
18,294 
11,069 

33,244 
62,514 

49,851 

60,602 
77,299 

78,231 

73,564 
71,766 
80,941 

Aver.    16,725 

48,536 

72,044 

76,434 

It  will  be  noticed  that,  whereas  without  sewage  the  amount  of 
green  grass  was  about  eight  tons  on  an  acre  and  a  quarter  in 
the  field,  from  lot  No.  2  twenty-four  tons  were  cut,  from  lot 
No.  3  thirty-six  tons,  and  from  lot  No.  4  thirty-eight  tons. 
Evidently  the  amount  of  sewage  applied  did  not  proportionately 
increase  the  yield  in  lots  3  and  4,  and  it  may  be  said  that  a 


104        PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

depth  of  sewage  or  water  of  more  than  twelve  inches  per  acre 
has,  in  general,  been  found  to  be  not  merely  unnecessary,  but 
undesirable.  The  table  does  not  show  the  number  of  cuttings 
made  during  the  season,  but  the  custom  on  the  farm  is  to  cut 
frequently,  at  intervals  of  perhaps  two  or  three  weeks,  no  time 
being  given  for  curing  the  hay. 

The  crops  suitable  for  growth  on  irrigated  fields  have  been 
found  by  experience  to  be  grass  and  root  crops,  such  as  beets, 
turnips,  and  the  like.  Mr.  Wilcox,  in  writing  of  the  require- 
ments of  different  plants,  suggests  celery  as  a  garden  crop  that 
needs  a  great  deal  of  water.  Beets,  carrots,  parsnips,  and  turnips 
are  favorite  plants  for  irrigated  fields.  Cabbage  and  cauli- 
flower are  benefited  by  abundant  irrigation  during  the  first  part 
of  their  growth,  but  after  the  heads  of  the  cabbage  plants  are 
half -formed,  further  excessive  use  of  water  is  undesirable. 
The  use  of  irrigating  water  in  orchards  has  been  practised  with 
great  success  not  only  in  the  recent  irrigation  areas  of  the  West, 
but  along  the  Hudson  River  and  in  New  England.  The  size 
of  the  fruit  is  increased  by  irrigation,  and  it  is  said  that  the 
bloom  is  much  improved. 

METHODS  or  APPLYING  THE  WATER 

In  distributing  the  water  or  sewage  over  the  soil  in  the 
case  of  a  single  house,  no  elaborate  methods  are  required.  In 
the  case  of  large  farms  supplied  with  sewage  from  a  considerable 
population,  elaborate  systems  of  piping  or  open-channel  con- 
duits are  required,  and  the  problem  of  working  out  and  adjusting 
the  necessary  sizes  and  grades  becomes  a  complicated  matter 
for  which  engineering  knowledge  and  experience  are  required. 
But  for  the  small  flow  which  comes  from  individual  houses  and 
from  the  small  area  involved,  no  such  elaborate  preparations 


BROAD   IRRIGATION  105 

are  required.  The  essence  of  the  distribution  consists  in  carrying 
the  water  onto  the  field  to  be  irrigated  at  such  a  low  velocity 
that  no  surface  soil  or  valuable  manures  are  washed  away; 
and  in  adjusting  the  volume  of  the  flow  and  the  requirements 
of  the  soil,  there  are  three  characteristic  conditions  which  require 
different  treatments. 

In  the  first  place,  the  area  may  be  practically  level  and  the 
crop  raised  may  be  either  grass  or  grain.  In  such  a  case  the 
sewage  should  be  led  onto  the  field  which  may  properly  be 
enclosed  on  four  sides  with  a  low,  that  is,  six  to  twelve  inches, 
earth-dike,  and  at  each  irrigation  the  field  may  be  flooded 
about  two  inches  deep.  The  next  irrigation  would  probably 
not  be  required  for  a  week,  so  that  this  method  requires  a  num- 
ber of  beds  to  be  worked  one  after  another  and,  except  where 
the  soil  is  very  dense,  so  much  so  that  percolation  is  very  slow, 
this  method  is  not  suitable  because  of  the  slow  rate  at  which 
the  sewage  is  delivered. 

The  second  method  of  distribution,  and  one  more  suitable  for 
the  conditions  under  discussion,  is  to  lay  out  the  field  in  parallel 
beds  from  three  to  six  feet  wide  and  from  forty  to  one  hundred 
feet  long.  These  beds  are  separated  by  furrows  into  which 
the  sewage  is  discharged.  If  the  grade  of  these  furrows  is 
properly  adjusted  to  the  porosity  of  the  soil,  that  is,  made  about 
six  inches  in  one  hundred  feet  for  open,  sandy  loam,  and  about 
two  inches  in  one  hundred  feet  for  fine,  clay  loam,  the  soil  will 
absorb  the  needed  moisture  as  the  sewage  flows  over  it  and 
there  should  be  no  ponding  or  excess  of  water  at  any  point  of 
the  field.  By  dividing  the  field  into  three  parts,  or  in  arranging 
the  flow  of  sewage  so  that  it  enters  only  two^or  three  furrows 
at  a  time,  the  flow  can  be  so  changed  from  day  to  day  as  to 
furnish  all  parts  of  the  area  with  the  irrigating  water,  and  at 
the  same  time  not  overload  and  choke  the  soil  particles.  On 


106        PRACTICAL   METHODS   OF   SEWAGE  DISPOSAL 

the  beds  may  be  planted  and  grown  whatever  vegetables  are 
desired.  A  good  basis  for  determining  the  area  and  length 
of  furrows  required  is  to  provide  a  length  of  thirty  feet  of  furrow 
for  each  person  of  the  household.  The  total  length  thus  obtained 
should  not,  however,  be  made  continuous,  but  should  be  arranged 
in  three  parts,  or  in  multiples  of  three,  so  that  one-third  of  the 
total  length  only  may  be  used  on  any  one  day,  the  other  parts 
serving  for  other  .days,  so  that  a  rotation  is  practised. 

The  third  condition  involves  the  application  of  the  sewage 
to  a  steep  slope,  and  this  may  be  treated  in  either  one  of  two 


FIG.  48. — Distribution  of  Sewage  and  Arrangement  of  Check  Levees  on  a 

Hillside. 

ways.  The  sewage  may  be  led  to  the  top  of  the  hill  and  allowed 
to  flow,  for  a  short  distance  only,  over  the  surface  on  which, 
presumably,  grass  is  to  be  grown.  If  the  length  of  the  furrow 
is  more  than  about  a  dozen  feet,  the  flowing  stream  acquires 
enough  velocity  to  wash  the  surface  and  to  form  gullies.  To 
prevent  this,  a  secondary  ditch  or  small  bank  is  thrown  up 
to  arrest  the  flow.  The  water  is  led  out  again  from  behind  this 
ditch  or  bank  at  intervals,  to  repeat  the  process  further  down  the 
hill  (see  Fig.  48).  If  the  slope  of  the  ground  is  moderate,  so 


BROAD   IRRIGATION 


107 


that  there  is  no  tendency  of  the  water  to  form  gullies,  the 
water  may  be  let  out  of  the  ditch  at  intervals  and  allowed  to 
distribute  itself  over  the  field,  as  shown  in  Fig.  49.  The  water 
thus  overflowing  should  be  collected  in  a  drain  at  the  lower 
end  of  the  slope,  and  will  be  found  suitably  purified  for  dis- 
charge into  any  running  stream  not  used  for  drinking  purposes. 
The  occasional  use  of  a  shovel  or  hoe  may  be  needed  to  change 
the  flow  of  the  water  over  the  field  if  it  is  found  that  any  ten- 
dency exists  for  definite  channels  to  be  formed. 


FIG.  49. — Distribution  of  Sewage  on  a  Hillside  of  Moderate  Slope. 

In  order  to  plant  vegetables  on  such  a  hill,  small  furrows 
may  be  made  along  the  hill  and  laid  out  with  great  care  so  that 
the  flow  of  sewage  in  the  furrows  shall  be  only  at  a  slow  velocity, 
so  slow  that  the  soil  can  absorb  the  moisture  as  the  water 
passes  along.  By  zigzagging  this  furrow  back  and  forth  down 
the  hillside,  vegetation  on  the  hill  will  receive  the  benefit  of  the 
water,  and  if  any  of  the  sewage  succeeds  in  reaching  the  bottom 
of  the  hill,  it  will  be  so  purified  that  it  may  be  safely  discharged 
into  any  depression  or  watercourse  there  found. 


108       PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 


PLAN 


= 

II 


•^illliiilliiiiililllimillli 


I  I 

i  i 


• 

I 

• 

si 


II I 

OH      5 


In  the  case  of  orchards,  irrigation  is  practised  by  flooding 
the  ground  around  the  tree,  being  careful,  however,  to  throw 
up  a  mound  of  earth  around  the  tree  so  that  no  water  comes 
within  two  feet  of  the  tree  itself.  Fig.  50  shows  a  Western 
method  of  forming  square  beds,  each  bed  about  twenty  feet 
on  a  side,  with  one  tree  at  the  centre.  Furrows  are  also  used 

to  distribute  the  water,  a  com- 
mon practice  followed  being  to 
have  the  furrow  always  under  the 
extreme  edge  of  the  foliage,  thus 
discharging  the  water  in  the  vicin- 
ity of  the  tender  rootlets  of  the 
tree.  Usually  the  furrow  system 
is  carried  only  in  one  direction,  so 
that  the  application  of  water  by 
this  method  is  not  so  complete  as 
by  the  flooding  method.  But  for 
small  volumes  of  water  constantly 
applied,  it  is  probably  more  satis- 
factory. Fig.  51  shows  a  grain  field 
irrigated  by  the  furrow  method. 
In  all  cases  where  irrigation  is 
practised,  stress  is  laid  by  those 
experienced  in  the  matter  on  the 
necessity  of  cultivation  of  the  soil 

in  connection  with  the  irrigation.  Apparently,  there  is  a  ten- 
dency for  the  surface  layers,  with  the  application  of  water,  to 
cake  or  crust  over  the  lower  strata,  thus  depriving  the  soil  of 
the  necessary  air.  In  order  to  break  up  this  crust,  the  soil 
must  be  continually  worked,  either  by  a  hoe  or  rake  or  some 
sort  of  horse  cultivator.  Where  the  ground  is  shaded,  as  in 
the  case  of  land  covered  with  grass  or  grain,  the  tendency  to 


=  i 

II 
\l 


iiiiiwiiiiiiiiiiiniiii 


SECTION  a-b 

FIG.  50. —  Square  Beds  for  Or- 
chards According  to  Some 
Western  Practice. 


BROAD    IRRIGATION 


109 


crust  is  not  so  marked,  but  on  cultivated  land  where  root 
crops  are  grown  the  cultivator  must  be  used  regularly 
after  each  irrigation.  Where  the  sewage  is  carried  onto  the 
field  in  furrows,  the  soil  in  the  furrow  should  be  hoed  at 
frequent  intervals,  not  only  to  break  up  the  crust  which  de- 


FIG.  51. — Grain  Field  in  Spring,  in  Process  of  Irrigation. 

prives  the  soil  of  the  air,  but  in  order  to  open  the  particles 
of  soil  for  the  reception  of  the  irrigating- water. 

It  must  also  be  remembered,  as  has  been  pointed  out  before, 
that  the  success  of  any  method  of  applying  sewage  to  soil 
depends  upon  the  frequent  change  from  bed  to  bed,  the  actual 
time  interval  depending  on  the  character  of  the  soil.  If  the  soil 
is  fine,  the  same  area  may  be  used  for  a  week  at  a  time,  and 
then  given  two  weeks'  rest.  If  the  soil  is  more  open,  this  interval 


110         PRACTICAL    METHODS    OF    SEWAGE    DISPOSAL 

should  be  reduced,  and  with  very  coarse  particles  it  may  be 
found  desirable  to  shift  the  flow  from  one  bed  to  another  after 
an  interval  of  a  few  hours  only.  Experience  and  careful  observa- 
tion on  the  moisture-carrying  capacity  of  the  bed  is  the  best 
guide  to  the  operation  of  sewage  irrigation. 

Whether  or  not  this  method  of  disposing  of  the  sewage  of 
a  single  house  is  to  be  selected  depends  largely  upon  the  slope  of 
the  ground  from  the  house  toward  the  garden.  It  is  not  desirable 
to  have  sewage  exposed  to  the  air  in  the  immediate  vicinity 
of  a  dwelling-house.  Rarely  would  any  odors  be  generated  to 
such  an  extent  as  to  be  offensive  to  the  occupants  of  the  house, 
since  the  sewage  sinks  into  the  ground  before  putrefaction  of 
the  organic  matter  sets  in  and  the  exposed  material  left  on  the 
surface  of  the  ground  is  of  too  attenuated  a  type  to  become 
offensive  even  if  it  does  putrefy  before  drying.  There  is,  how- 
ever, the  danger  of  odors  being  formed  where  distribution  is 
imperfect  and  where  pools  are  allowed  to  form  in  the  furrow. 
There  is  also  the  danger  of  the  transmission  of  disease  germs 
from  the  sewage-irrigated  field  to  the  occupants  of  the  house 
through  the  agency  of  flies.  Health  statistics  of  English  farms 
show  this  danger  to  be  a  very  remote  one,  since  the  health  of 
the  workman  on  those  farms  is  as  good  or  better  than  the 
average  throughout  England.  But  the  possibility  of  infection 
exists  and  must  not  be  overlooked. 

No  method  of  disposal  requires  so  much  and  such  constant 
care,  although  the  results  show  in  the  improved  yield  from  the 
farm.  This  method  of  broad  irrigation  is  emphatically  not  the 
method  to  be  used  except  where  labor  is  adequate  for  proper 
soil  cultivation  and  where  this  labor  can  be  given  constantly 
and  ungrudgingly.  Finally,  it  must  be  pointed  out  that  care 
should  always  be  exercised  to  prevent  irrigating  sewage  coming 
in  direct  contact  with  any  of  the  soil  produce.  Certainly  sewage 


BROAD   IRRIGATION       .  Ill 

should  not  be  used  to  sprinkle  over  lettuce  or  celery  or  straw- 
berries, even  if  the  yield  is  thereby  increased.  Undoubtedly 
any  disease  germs  thus  distributed  over  the  fruits  and  vegetables 
would,  through  the  antiseptic  action  of  the  sunlight  and  air, 
soon  be  destroyed,  but  the  very  method  of  irrigation  is  repulsive, 
and  the  danger,  while  slight,  is  sufficient  to  forbid  that  method 
of  fertilizing.  No  statistics,  however,  are  available  to  show 
that  cows  eating  sewage-irrigated  grass  are  adversely  affected 
in  health,  and  for  years  the  practice  of  thus  pasturing  cows 
has  been  carried  on  in  England.  For  human  beings,  however, 
vegetables  grown  in  soil  that  is  separated  from  the  sewage  by  a 
foot  or  more  is  the  safer  as  well  as  more  aesthetic  arrangement. 


CHAPTER  VII 
ESTIMATES    OF    COST 

In  order  to  estimate  the  cost  of  installing  a  sewage-disposal 
plant  and  of  treating  continuously  the  sewage  from  any  resi- 
dence, certain  fundamental  assumptions  are  always  necessary. 
In  the  first  place,  the  unit  cost  of  the  manual  labor  which  forms 
so  large  a  part  of  the  total  cost  of  construction  must  be  known 
for  the  particular  time  and  place,  and  perhaps  no  item  in  the 
cost  of  construction  is  so  important  as  this.  In  a  great  many 
small  installations  it  may  be  excluded  altogether,  since  all  the 
hand  work  required  is  contributed  by  the  householder  at  such 
times  as  the  other  work  of  the  place  may  allow,  without  any 
additional  cost.  In  other  places,  if  a  money  value  be  placed 
on  such  labor,  it  may  be  expressed  in  terms  of  the  cost  of  a 
hired  man  whose  rate  of  wages,  paid  monthly,  in  addition  to 
board,  would  be  always  less  than  if  wages  were  paid  to  day 
laborers  living  at  their  own  homes.  Again,  in  the  southern 
part  of  the  country  labor  may  be  had  for  $1.25  a  day,  whereas 
in  the  central  portion  of  the  United  States  it  is  necessary  to  pay 
$1.75  a  day,  and  in  the  extreme  West  from  $2.00  to  $3.00  a  day 
for  common  labor.  Often,  too,  the  working  day  is  of  different 
length  in  different  parts  of  the  country.  In  the  estimates  which 
follow,  labor  is  assumed  to  cost  $1.60  for  eight  hours'  work, 
that  is,  at  the  rate  of  twenty  cents  an  hour.  If,  in  adapting 
the  estimates  of  this  chapter  to  any  particular  installation,  the 
question  of  labor  may  be  neglected  because  of  the  fact  that  the 
householder  will  himself  do  all  the  required  work,  then  the  item 
of  labor  cost  may  be  eliminated.  If  other  units  than  those 
here  assumed  are  suitable  for  the  particular  locality  where 

112 


ESTIMATES    OF   COST  113 

any  plant  is  to  be  built,  then  the  labor  item  must  be  modified 
accordingly. 

Material. — The  cost  of  material  always  varies  very  greatly  in 
different  parts  of  the  country.  This  is  partly  because  of  different 
freight  and  other  transportation  rates  between  the  factories 
where  material  is  made  up  and  the  particular  place  where  that 
material  is  to  be  used;  and  partly  because  the  profits  made 
by  the  middleman  increase  as  the  material  gets  further  and 
further  away  from  the  centres  of  civilization.  Thus,  in  a  large 
city  six-inch  sewer  pipe  may  be  sold  in  such  large  quantities 
that  the  freight  rate  is  low  and  the  dealer  is  satisfied  with  a 
small  profit  on  each  foot  of  pipe.  In  the  country  districts  the 
dealer  sells  but  little,  and  feels  that  he  must  have  a  larger  profit 
to  compensate  him  for  the  expense  of  keeping  the  material  on 
hand.  Thus,  six-inch  sewer  pipe  may  be  had  at  prices  ranging 
from  six  cents  up  to  sixteen  cents  per  running  foot,  depending 
on  the  store  from  which  it  is  bought. 

It  is  evident,  therefore,  that  it  will  not  be  possible  to  name 
any  unit  price  which  will  be  generally  applicable,  and  it  will 
be  necessary  for  any  intending  builder  to  secure  from  local 
firms  the  unit  prices  from  which  his  own  individual  estimate 
may  be  made  up.  The  following  discussion,  however,  will 
indicate  the  items  comprising  the  necessary  estimate,  and  will 
furnish  an  example  by  which  the  estimate  sheet  can  be  prepared. 

Laying  Sewers  and  Drains. — The  main  drain  from  the  house 
to  the  sewage  disposal  plant  is  of  five-  or  six-inch  pipe  generally, 
the  former  being  sufficiently  large  and  a  little  cheaper  than  the 
six-inch  pipe.  The  latter  has  the  advantage  of  size  and  conse- 
quent greater  freedom  from  clogging.  The  cost  of  five-inch  pipe 
at  a  store  in  a  village  of  any  considerable  size  should  be  ten 
cents  per  foot,  and  the  cost  of  six-inch  pipe  twelve  cents  per  foot. 

This  pipe  weighs  twelve  and  fifteen  pounds  per  foot  respec- 


114        PRACTICAL   METHODS   OF   SEWAGE   DISPOSAI 

tively,  and,  with  an  ordinary  wagon,  fifty  feet  of  six-inch  pipe, 
weighing  about  eight  hundred  pounds,  is  a  load;  if  four  trips  a 
day  are  possible  from  the  residence  to  the  store  and  if  the  cost 
of  the  team  is  estimated  at  $4  a  day,  each  trip  will  cost  $i, 
and  each  foot  of  pipe  will  cost  two  cents  more  for  being  hauled 
from  the  store  to  the  grounds. 

In  laying  the  pipe,  cement  and  sand  are  necessary  for  joints. 
For  both  kinds  of  pipe  there  is  required  about  one  cubic  foot 
of  mortar  for  each  fifty  joints,  the  mortar  being  sufficient  to 
fill  the  joints  and  to  make  a  collar  or  ring  outside.  In  order  to 
make  this  cubic  foot  of  mortar,  half  a  bag  of  cement  and  half  a 
cubic  foot  of  sand  will  be  required.  The  cost  of  the  cement  out 
of  the  village  store  is  about  fifty  cents  a  bag,  although  in  a 
small  place  it  may  be  seventy-five  cents,  or  even  one  dollar. 
If  one  were  buying  cement  in  large  quantities,  a  price  as  low 
as  thirty  cents  a  bag  might  be  had.  If  the  cement  is  delivered 
in  cloth  bags,  a  rebate  of  ten  cents  a  bag  is  usually  given  if  the 
bag  is  returned  in  good  condition. 

The  cost  of  sand  is  usually  dependent  upon  the  cost  of  hauling. 
It  will  require  forty  minutes  to  shovel  one  yard  of  sand  into 
a  wagon,  or  at  twenty  cents  an  hour  it  would  cost  about 
fifteen  cents.  The  cost  of  shovelling  sand  through  a  screen 
depends  upon  the  amount  of  material  which  has  to  be  rejected, 
since  only  a  certain  proportion  of  the  sand  is  available  for  all  that 
is  shovelled.  The  cost  of  this  shovelling  is  again  about  fifteen 
cents  per  cubic  yard  of  material  shovelled,  and  if  one-third  of  it 
is  coarse  gravel  which  has  to  be  rejected,  one  and  one-half 
yards  would  have  to  be  screened  for  every  yard  of  sand  available, 
and  the  cost  would,  therefore,  be  twenty  cents  for  screening, 
a  total  cost  of  sand  in  the  wagon  of  thirty-five  cents  per  yard. 
If  four  loads  of  sand  can  be  delivered  per  day,  with  a  cost  of 
fifty  cents  per  hour  for  team  and  driver,  the  sand  will  cost 


ESTIMATES   OF   COST  115 

$1.35  per  yard  on  the  grounds,  this  amount  being  increased  or 
decreased  if  the  number  of  trips  per  day  must  be  made  less 
or  more. 

Excavation. — The  cost  of  excavation  depends  on  the  char- 
acter of  the  material  and  on  the  amount  of  water  present,  the 
cost  of  pumping  or  bailing  the  latter,  if  in  large  quantity,  adding 
materially  to  the  cost  of  shovelling.  The  material  through 
which  the  trenches  are  driven  may  vary  from  a  sand  which  can 
be  shovelled  without  loosening,  to  solid  rock  which  must  be 
blasted,  an  intermediate  condition  of  soil  being  known  as  hard- 
pan  and  its  excavation  costing  nearly  as  much  time  and  effort 
as  rock  itself.  If  the  soil  is  sand,  into  which  a  shovel  or  spade 
can  be  pushed  without  any  picking  of  the  material,  the  cost, 
as  already  stated,  will  be  about  fifteen  cents  a  cubic  yard  for 
shovelling,  and  if  the  excavation  is  in  trench  and  not  more  than 
six  feet  deep,  the  entire  trench  can  be  excavated  for  seven 
and  a  half  cents  a  lineal  foot.  It  is  very  unusual,  however, 
to  have  conditions  so  favorable  that  such  a  low  price  can  be 
counted  on.  If  the  material  requires  picking,  instead  of  fifteen 
cents  a  cubic  yard  it  will  cost  thirty  cents  a  cubic  yard,  and  a 
trench  two  feet  wide  and  six  feet  deep  will  cost  fifteen  cents  a 
running  foot  instead  of  seven  and  a  half  cents.  If  care  is  not 
taken  at  the  start  to  throw  the  dirt  well  back,  it  will  be  necessary 
to  re-handle  the  dirt  from  the  bottom  of  the  trench,  throwing 
it  back  on  the  pile,  and  this  will  add  from  five  to  ten  cents  a 
cubic  yard,  depending  on  what  proportion  of  the  entire  excavation 
has  to  be  re-handled.  In  the  excavation  for  a  tank,  it  is  quite 
possible  that  the  entire  material  may  have  to  be  re-handled  and 
the  cost  thus  be  increased  by  fifteen  cents  a  cubic  yard.  If  the 
ground  is  very  hard,  as  when  boulders  and  clay  are  intermixed, 
it  may  require  twice  as  much  time  for  loosening  as  for  shovelling, 
in  which  case  the  cost  of  digging  the  trench  will  be  forty-five  cents 


116       PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

a  cubic  yard,  or  twenty-two  and  a  half  cents  per  lineal  foot, 
with  five  or  ten  cents  added  if  the  material  has  to  be  re-handled. 

If  the  material  is  a  loose  sand  or  gravel,  the  trench  will 
probably  require  sheeting,  that  is,  boards  or  planks  on  each 
side  of  the  open  trench  with  braces  between,  in  order  to  prevent 
caving  of  the  banks.  If  new  lumber  has  to  be  purchased  for 
this  purpose  and  its  cost  added  to  the  cost  of  excavation,  an 
additional  sum  per  cubic  yard  or  per  lineal  foot  will  be  added, 
somewhat  in  proportion  to  the  total  amount  of  excavation 
to  be  done.  Finally,  if  the  soil  through  which  the  trench  is 
being  dug  contains  water,  it  may  be  necessary  to  have  one  or 
two  men  continuously  pumping  during  all  the  time  that  the 
excavation  is  going  on,  and  this  also  will  add  to  the  cost  per 
cubic  yard  or  per  lineal  foot  of  the  trench. 

Refilling  may  be  done  by  hand  or  may  be  done  by  a  drag 
scraper  at  the  end  of  a  rope,  so  that  the  team  of  horses  may  be 
on  one  side  of  the  trench  and  draw  into  it  from  the  other  side 
the  excavated  material.  This  costs  only  five  cents  per  cubic 
yard.  If  the  dirt  is  thrown  back  by  hand,  the  cost  will  be  that 
of  shovelling,  namely,  about  fifteen  cents  per  cubic  yard.  If  the 
dirt  has  to  be  tamped  in  the  trench,  the  cost  will  then  be  that 
of  another  man,  and  backfilling  will  often  add  thirty  cents  a 
cubic  yard  to  the  cost  of  excavation. 

As  a  summary,  it  may  be  said  that  excavation  alone  in  earth 
may  cost  from  fifteen  cents  to  forty-five  cents  a  cubic  yard, 
and  that  backfilling  may  add  to  this,  from  five  to  thirty  cents 
a  cubic  yard,  the  entire  cost,  therefore,  varying  from  twenty 
cents  to  seventy-five  cents  a  cubic  yard  for  excavation  and  back- 
filling together.  Nor  is  it  possible  to  be  more  definite  in  explain- 
ing the  proper  price  to  put  on  excavation  since  the  character 
of  the  material  and  the  nature  of  the  excavation  are  of  such 
importance  in  fixing  that  cost.  If  the  excavation  is  for  a  tank, 


ESTIMATES   OF   COST  117 

it  is  often  possible  to  rig  a  derrick  with  a  long  arm  on  the  side 
of  the  excavation  and,  by  means  of  a  bucket,  transfer  the 
excavated  material  from  the  hole  to  the  bank  cheaper  than 
by  repeated  shovelling  or  by  carrying  out  the  dirt  in  a  wheel- 
barrow. Wheelbarrow  work  is  always  expensive,  the  cost  of 
transporting  earth  in  a  wheelbarrow  a  distance  of  fifty  feet 
being  about  ten  cents  a  cubic  yard.  Sometimes  a  horse  may  be 
used  to  great  advantage  to  lift  the  bucket  and  operate  the 
derrick  in  place  of  a  hand-worked  windlass,  although  the  use 
of  the  horse  is  hardly  worth  while  unless  the  excavation  is  more 
than  ten  feet  deep. 

The  excavation  for  the  trenches  of  a  sub-surface  irrigation 
system  cannot  be  estimated  on  the  same  basis  as  for  a  larger 
trench.  More  time  is  required  proportionally  in  trimming  and 
grading  the  sides  and  bottom,  so  that  the  cost  per  cubic  yard 
is  much  increased.  Thus,  while  such  trenches  contain  about 
one  cubic  foot  of  earth  per  lineal  foot,  and  on  the  basis  of  twenty- 
seven  cents  per  yard  would  cost  only  one  cent  per  lineal  foot 
to  dig,  it  is  probable  that,  under  ordinary  conditions,  this 
amount  would  be  doubled. 

The  cost  of  underdrains  must  be  made  up  from  the  cost 
of  the  pipe  used  and  the  cost  of  the  necessary  excavation.  In  the 
bottom  of  artificial  filter  beds,  the  latter  amounts  to  little  or 
nothing.  In  natural  filter  beds,  the  trenches  are  deeper  and 
the  cost  of  the  underdrainage  depends  largely  on  this  excava- 
tion cost.  The  cost  of  the  pipe  varies  from  two  to  ten  cents 
per  foot,  depending  on  the  kind  of  pipe  used  and  its  unit  cost. 

Rock  Excavation. — If  the  trench  or  the  place  for  the  tank  is 
to  be  in  rock,  the  cost  of  excavation  is  much  increased.  The  rock 
must  be  drilled  and  blasting  powder  or  dynamite  used  to  loosen 
the  material  so  that  it  can  be  thrown  out  later  by  hand.  In 
ordinary  rock,  a  man  will  drill  from  six  inches  to  twelve  inches 


118        PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

of  hole  per  hour,  that  is,  the  hole  will  cost  from  ten  to  twenty 
cents  per  lineal  foot.  The  depth  of  the  hole  determines  the 
amount  of  rock  loosened  per  charge.  If  the  holes  are  three 
feet  deep,  about  one-third  of  a  cubic  yard  is  loosened  per  hour, 
while  if  the  holes  are  five  feet  deep,  one  cubic  yard  of  rock  is 
loosened  per  hour.  This  indicates  at  once  the  economical 
advantage  of  deep  holes  compared  with  shallow  ones.  In  the 
first  case,  nine  lineal  feet  of  hole  would  have  to  be  drilled  in 
order  to  get  one  cubic  yard  of  rock,  nearly  double  the  amount 
required  where  the  hole  is  five  feet  deep.  Usually  the  distance 
between  the  holes  is  made  equal  to  the  depth  of  the  holes, 
although  in  some  rock  the  depth  can,  with  advantage,  be  made 
greater  than  that  distance.  If  the  rock  is  very  loose  and  seamy, 
deep  holes  may  sometimes  not  be  warranted,  because  the  effect 
of  the  blasting  is  taken  up  by  the  loose  rock  in  such  a  way  that 
the  value  of  the  explosive  is  not  realized.  Shallower  holes, 
more  frequently  blasted,  utilize  the  explosive  gases  more  com- 
pletely. 

The  kind  of  explosive  which  may  be  used  varies  from  slow, 
low-power  black  powder  to  rapid,  high-power  nitro-glycerine, 
the  many  forms  of  dynamite  and  high-grade  powder  in  use 
being  combinations  of  nitro-glycerine  with  some  absorbent.  In 
most  cases,  ordinary  blasting  powder  is  suitable  for  rock  excava- 
tion in  small  quantity.  It  lifts  the  rock  rather  than  shatters  it, 
and  is  more  convenient  and  safe  to  handle.  Forty-per-cent 
dynamite  is  to  be  recommended  where  the  rock  is  very  seamy 
so  that  quick-acting  explosive  is  essential,  and  also  where  the 
rock  is  very  hard,  so  that  black  powder  tends  to  blow  out  the 
hole  rather  than  to  shatter  the  rock.  The  cost  of  forty-per- 
cent dynamite  is  about  twenty  cents  per  pound,  and  the  cost 
of  powder  is  about  twelve  cents  per  pound.  On  the  average, 
it  may  be  assumed  that  it  will  require  one  pound  of  the  former 


ESTIMATES   OF   COST  119 

and  one  and  a  half  pounds  of  the  latter  per  cubic  yard  of  ordinary 
rock  excavated.  The  cost  of  lifting  the  blasted  material  out 
of  the  trench  will  be  at  about  the  same  rate  as  that  of  earth. 

Concrete. — The  walls  of  tanks  made  of  concrete  depend  for 
their  cost  upon  the  cost  of  the  material  and  the  cost  of  the  labor 
involved.  It  is  usually  more  economical  to  use  gravel  as  the 
basis  of  the  concrete  if  any  is  available,  and  in  order  that  the 
product  may  be  of  good  quality  it  is  always  best  to  screen  this 
gravel,  separating  it  into  sand  and  stone.  The  proper  size  of 
screen  for  this  operation  should  be  not  greater  than  one-half- 
inch  mesh.  The  stone  and  sand  can  then  be  re-combined  with 
the  cement  in  the  proportion  of  one  part  of  cement  to  two  and 
a  half  parts  of  sand  to  five  parts  of  stone,  this  mixture  making 
a  very  strong  and  impervious  combination.  The  cost  of  this 
mixture  depends  chiefly  on  the  length  of  haul  for  the  gravel 
and  on  the  natural  grading  of  the  material.  ,  If  the  proportions 
required  for  concrete  exist  naturally  in  the  bank  or  stream  bed 
from  which  the  gravel  is  to  be  obtained,  there  is  little  or  no  waste 
involved  in  screening,  and  the  only  cost  is  that  of  handling  the 
material  twice.  If,  on  the  other  hand,  the  amount  of  stone 
is  inadequate,  it  may  be  necessary  to  waste  a  good  deal  of  the 
fine  sand  and  enough  material  has  to  be  shovelled  to  produce 
the  required  amount  of  coarse  media.  Assuming  that  the  cost 
of  shovelling  the  material  from  the  stream  bed  is  fifteen  cents 
a  cubic  yard,  and  that  the  haul  is  two  miles,  so  that  four  trips 
a  day  are  made,  then  the  gravel  can  be  delivered  where  it  is 
to  be  converted  into  concrete  at  a  cost  of  one  dollar  for  hauling 
and  thirty  cents  for  shovelling,  while  if  the  haul  is  only  one  mile, 
so  that  eight  trips  a  day  can  be  made,  the  cost  will  be  eighty 
cents  per  cubic  yard.  If  any  waste  of  gravel  is  necessary,  these 
costs  will  be  increased  correspondingly. 

At  the  site  of  the  proposed  plant  the  sand  and  gravel  must 


120        PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

be  mixed  with  the  cement  and  carried  to  place.  It  has  been 
found  by  experience  when  the  mixing  is  done  thoroughly  and 
by  hand,  and  when  the  resulting  concrete  can  be  shovelled 
directly  behind  the  forms,  that  the  cost  of  the  mixing  and  placing 
is  about  one  dollar  per  cubic  yard  of  concrete.  If  the  concrete 
has  to  be  wheeled  into  place  this  cost  will  be  added  to. 

In  order  to  make  a  cubic  yard  of  concrete,  it  is  necessary 
to  have  nearly  one  cubic  yard  of  the  coarse  material,  whether 
this  be  rounded  stones  from  a  gravel  bank  or  angular  stones 
from  a  stone-crusher.  Seven-eighths  of  a  cubic  yard  of  stone 
may  be  safely  considered  as  necessary  for  a  cubic  yard  of  con- 
crete.. To  this  must  be  added  three-eighths  of  a  cubic  yard 
of  sand  for  a  one  to  two  and  a  half  to  five  mixture.  When  this 
amount  of  stone  and  sand  have  been  thoroughly  mixed  together, 
four  and  a  half  bags  of  cement  should  be  added.  Inasmuch  as 
the  variation  in  sizes  of  the  individual  particles  of  rounded 
gravel  is  such  that  a  dense  concrete  results  naturally,  it  is  quite 
reasonable  both  to  increase  the  amount  of  stone  and  decrease 
the  amount  of  cement  if  that  variation  in  size  seems  to  be 
one  which  will  produce  a  dense  mixture.  Thus  one  cubic,  yard 
of  stone,  one-third  cubic  yard  of  sand,  and  four  bags  of  cement 
may  be  used  and  will,  under  favorable  conditions,  result  in  a 
good  concrete.  In  order  to  determine  whether  this  latter  com- 
bination is  permissible  on  any  particular  piece  of  work,  a  test 
may  be  made  by  thoroughly  mixing  the  materials  together  in 
the  proportions  named  and  testing  the  volume  of  this  mixture 
(B)  in  a  box  of  measured  dimensions.  Then  the  same  volumes 
mixed  together  in  the  former  proportions  (mixture  A),  and 
tested  in  the  same  box  will  show  the  relative  value  by  occupying 
either  more  or  less  space  than  the  other  mixture  (B).  If  less, 
mixture  A  is  a  better  one,  and  should  be  used;  if  more,  then 
the  latter  mixture,  B,  is  the  better  one. 


ESTIMATES   OF   COST  121 

The  amount  of  water  required  for  mixing  concrete  depends 
upon  the  temperature  of  the  outside  air  as  well  as  upon  the  per- 
sonal ideas  of  the  person  in  charge  of  the  mixing.  Some  builders 
like  wet  concrete  and  some  like  dry  concrete.  It  should  be 
noticed,  however,  that  wet  concrete  is  cheaper  because  it  requires 
little  or  no  tamping.  Wet  concrete,  however,  should  be  spaded, 
that  is,  a  spade  forced  down  into  the  mixture,  particularly 
against  the  forms,  so  that  particles  of  air  caught  between  the 
stones  may  escape,  and  so  that  there  may  be  no  pockets  between 
the  stones  into  which  the  liquid  cement  mixture  does  not  pene- 
trate. It  is  generally  considered  that  about  fifteen  per  cent  of 
the  volume  of  concrete  is  the  necessary  volume  of  water  for  the 
mixture.  This  amounts  to  thirty  gallons,  or  a  barrel  of  water, 
to  a  yard  of  concrete,  although  the  sizes  of  barrels  vary,  and  a 
cement  barrel  would  not  be  large  enough,  and  a  road-oil  barrel 
would  be  too  large. 

The  cost  of  forms  depends,  again,  on  the  cost  of  material 
and  on  the  cost  of  labor.  Rough  lumber  varies  in  price  from 
twenty  to  forty  dollars  a  thousand  feet,  board  measure,  de- 
livered on  the  grounds,  and  the  cost  of  framing  and  placing  it 
varies  from  eight  to  twenty  dollars  per  thousand,  depending 
on  the  skill  of  the  carpenters  and  on  their  daily  wages.  In  order 
to  estimate  the  cost  of  the  lumber  required  for  building  false 
work,  it  is  best  to  determine  exactly  the  amount  of  lumber 
required,  and  get  the  price  from  a  lumber  yard  on  that  quantity. 
Ordinarily,  it  is  safe  to  say  that  a  carpenter  in  building  forms 
will  be  able  to  saw  and  nail  in  place  250  board  feet  per  day,  so 
that,  knowing  the  amount  of  lumber  to  be  used  and  the  wages 
of  the  carpenter,  it  will  be  easy  to  determine  the  cost  of  the 
forms  as  first  set  up.  They  may  be  taken  down  and  removed  for 
the  purpose  of  re-assembling  in  another  place  for  about  half  the 
cost  of  placing  originally,  and  by  carefully  arranging  to  build  the 


122        PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

forms  in  panels  or  sections,  they  may  be  removed  by  a  carpenter 
at  the  rate  of  4,000  or  5,000  board  feet  per  day. 

Valves. — In  connection  with  a  sewage-disposal  plant,  valves 
are  essential  at  many  points.  At  the  entrance  to  the  several 
parts  of  the  settling  tank,  flap  valves  are  suitable  to  admit  or 
keep  out  sewage  from  the  several  compartments.  Gate  valves 
are  used  on  the  by-pass  lines  and  on  connecting  lines  between  the 
tank  and  the  filter  beds  in  order  to  be  of  service  when  it  is 
occasionally  necessary  to  clean  the  beds.  More  simple  valves 
may  be  used  in  manholes  where  a  diversion  of  the  flow  is  required 
and  where  perfect  and  complete  water- tightness  is  not  essential. 
These  valves  may  be  made  of  plank,  sliding  up  and  down  in 
grooves  left  in  the  concrete  walls  for  that  purpose.  Sludge  valves 
may  be  made  to  fit  in  the  bottom  of  the  tank,  and  depend  for 
their  water-tightness  on  the  weight  of  the  valve  itself  with  the 
aid  of  a  rubber  packing  which  is  placed  between  the  valve  and 
its  setting.  The  cost  of  these  various  kinds  of  valves  cannot 
be  given  exactly,  since  their  cost  depends  upon  freight  and 
profit  of  the  various  commission  men  through  whom  the  valves 
are  ordered,  but,  generally  speaking,  they  will  be  found  to  differ 
but  little  from  the  costs  given  in  the  following  table: 

TABLE 

Flap  valve  as  shown  in  Fig.  16 $5.00 

Gate  valve  (iron  bearings)  for  6-inch  pipe  (Fig.  13) 20.00 

Gate  valve  (bronze  bearings)  for  6-inch  pipe 30 .  oo 

Sludge  valve  as  shown  in  Fig.  10 4.00 

Iron  slide  valve  as  shown  in  Fig.  1 1 15 .  oo 

Dosing  Devices. — Dosing  devices  referred  to  in  Chapter  III 
are  usually  purchased  directly  from  the  manufacturer,  and  while 
their  cost  varies  a  little,  depending  upon  the  cost  of  freight, 
.an  ordinary  single  automatic  siphon  may  be  estimated  at  $15, 
•the  difference  in  price  varying  a  little  with  the  different  makes 


ESTIMATES   OF   COST  123 

of  siphon.  If  an  alternate  discharge  is  required,  then  two  siphons 
must  be  installed,  by  means  of  which  alternate  intermittency 
is  secured,  the  variation,  however,  being  only  from  one  to  the 
other  and  back  again  to  the  first.  If  a  plural  alternate  discharge 
is  to  be  used,  the  cost  may  be  estimated  roughly  for  a  6-inch 
siphon  at  from  $50  to  $75  for  each  unit,  this  price  including  the 
necessary  piping  but  not  the  cost  of  setting. 

Filling.  Material. — Artificial  sand  filters  require  a  sand  of 
uniform  size  and  one  free  from  dirt.  These  two  requirements 
add  very  materially  to  the  cost  of  sand,  since  it  is  almost  impos- 
sible to  find  a  natural  sand  which  fulfils  the  necessary  require- 
ments. A  few  sections  of  the  country  are  fortunate  in  having 
sand  in  the  vicinity  suitable  for  filtration  purposes  without 
any  washing  or  screening.  Such  parts  of  the  country,  however, 
are  limited  to  those  where  sand  has  been  deposited  by  glacial 
action,  and  is  essentially  silicious  in  character.  It  is  hopeless 
to  expect  to  find  suitable  sand  in  the  centre  of  New  York  State, 
for  example,  and  even  with  washing  and  screening,  sand  in  this 
locality  is  far  from  being  desirable.  It  will  be  found,  further, 
that  after  this  undesirable  sand  is  washed  and  screened  the 
cost  of  the  final  product  is  so  great  that  it  is  usually  cheaper 
to  use  broken  stone  either  as  a  filter  or  as  a  contact  bed. 

Washing  sand  in  small  quantities  is  done  by  throwing  the 
sand  into  a  channel  through  which  water  is  passing,  the  sand 
being  retained  by  a  series  of  low  partitions  in  the  channel. 
If  the  water  enters  the  box  or  channel  through  a  pipe  at  the 
bottom,  frequent  entrance  holes  being  provided  along  the  sides 
and  bottom  of  this  pipe,  the  sand  is  kept  in  a  state  of  suspension, 
the  dirt  more  readily  washed  out,  and  a  much  smaller  amount 
of  water  used.  The  cost  of  shovelling  the  sand  into  the  washer 
and  again  out  of  the  washer,  about  thirty  cents  per  cubic  yard, 
must  be  added  to  the  original  cost  of  the  sand.  The  cost  of 


124        PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

water,  if  pumped  by  hand  or  by  steam,  will  be  about  ten  cents 
per  cubic  yard  of  sand  cleaned,  making  the  total  cost  about 
forty  cents  per  cubic  yard.  If  only  three-fourths  of  the  unwashed 
sand  is  available  for  use,  then  the  cost  of  the  final  product 
is  a  little  less  than  fifty  cents  per  cubic  yard.  The  sand  before 
being  brought  to  the  washer  will  have  been  sifted  at  an  addi- 
tional cost  of  perhaps  thirty  cents  per  cubic  yard.  Hauling 
from  the  bank  to  the  washer,  or  from  the  washer  to  the  site  of 
the  disposal  works,  or  both,  if  the  water  supply  requires  the 
washer  to  be  placed  at  some  distance  from  the  sand  bank,  will 
add  from  fifty  cents  to  one  dollar  a  yard  to  the  costs  already 
indicated.  It  may  generally  be  assumed  that  it  will  be  im- 
possible to  put  sand  into  an  artificial  filter  for  less  than  $1.50  a 
cubic  yard,  and  it  may  easily  cost  $2.50  a  yard  if  the  sand  bank 
is  at  considerable  distance  from  the  site  of  the  works. 

Broken  stone  in  most  parts  of  the  country  can  now  be  bought 
from  a  stone-crushing  plant.  If  road  construction  has  been  in 
progress  in  the  vicinity,  the  contractor  for  the  work  has  been 
obliged  to  open  a  quarry  and  set  up  a  crushing-and-screening 
plant,  and  it  will  generally  be  possible  to  buy  broken  stone 
from  such  a  contractor  at  about  fifty  cents  per  cubic  yard. 
The  cost  of  hauling  and  the  cost  of  shovelling  into  the  beds  must 
be  added  to  determine  the  cost  of  the  stone  in  place.  Sometimes 
it  is  cheaper  to  bring  the  stone  from  a  distance  by  rail,  such  stone 
costing  about  $1.25  at  the  railroad  station.  Then  the  cost  of 
hauling  and  shovelling  must  be  added.  It  will  be  noticed  that 
the  cost  of  stone  does  not  differ  materially  from  the  cost  of  sand, 
and  since  the  amount  of  stone  needed  is  only  about  one-quarter 
of  the  sand  needed,  it  is  generally  cheaper  to  build  a  stone  bed. 
The  purification,  it  will  be  remembered,  however,  is  decidedly 
inferior. 

Finishing. — There  is  always  some  slight  expense  necessary  in 


ESTIMATES   OF   COST 


125 


finishing  and  cleaning  up  after  any  piece  of  construction  work. 
Material  left  over  has  to  be  hauled  away,  and  in  order  to  leave 
the  plant  in  an  attractive  dress,  seeding  or  sodding  the  earth 
slopes  is  desirable.  It  is  even  desirable  to  plant  shrubbery 
around  the  edges  of  the  beds,  partly  as  a  screen  and  partly  to 
minimize  the  offensive  suggestions  which  seem  to  be  inseparable 
from  any  plant  dealing  with  sewage.  The  cost  of  these  final 
improvements  may  be  as  little  or  as  much  as  the  owner  and 
builder  chooses,  but  it  is  urged  that  their  value  should  not  be 
overlooked. 

The  following  table  is  given  as  a  guide  and  help  in  putting 
together  the  various  items  that  make  up  the  total  cost  of  a 
sewage-disposal  plant.  Each  line  should  be  carefully  considered, 
and  if  the  item  mentioned  is  to  be  used  or  paid  for,  the  amount 
in  the  last  column  should  be  filled  out. 

TABLE  OF  ITEMS  ON  WHICH  TO  BASE  ESTIMATE  OF  COST  OF 
SEWAGE-DISPOSAL   PLANT 


Excavation  and  Refitting 

Trenches  in  sandy  soil,  shallow  depth  .  .          .  .  at  .    .  .  p< 
"  stiff       " 

*rcu.yd. 

it 

lin.  ft. 

« 

« 

sr  sq.yd. 
junt 

No.  of 

Units 

Cost 



"         "  sandy    "    deep  cut 

"  stiff      /'        "      "             
Tank  depth  and  soil  duly  considered 

.... 

.... 

Beds,       "       "       "     "               " 

Embankments  between  filter  beds  (additional 
cost) 

Trenches  for  sub-surface  lines 

"  underdrains 

"  sludge  disposal 

Surfacing  and  Finishing 
Surface  soil  placed  at  n« 

Gravel  in  walks  ' 

7                   «.! 

Dtal  am< 

Flowers  and  shrubbery                                        T 

126        PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 
TABLE  OF  COST.— Continued. 


Concrete  Work 


Manholes  on  pipe  lines at  ....  each 

Settling  tank,  bottom,  sides  and  roof "  .  .  . .  per  cu.yd 

Dosing  tank,  in  addition  to  settling  tank "  .  .  .  .    " 

Manholes  on  sub-surface  lines "  .  .  .  .    " 

Concrete  in  contact  beds  or  niters "  . . . .    " 

Concrete  in  protection  wall  at  end  of  outfall ...  "  . . . .   " 

Pipe  Lines 

5-  or  6-inch  tile  pipe  (laid),  house  to  disposal 

plant at  ....  per  lin.  ft 

6-inch  pipe  used  in  disposal  plant,  laid "  .  . .  .   " 

6-inch  pipe  from  plant  to  outfall "  . . . .   " 

6-inch  pipe  for  sludge  line "  .  .  . .    " 

6-inch  pipe  for  main  underdrain "  . . .  .    " 

3-inch  agricultural  tile  in  sub-surface  disposal.  "  .  .  .  .    " 

4-inch  agricultural  tile  in  underdrains "  .  .  .  .    " 

6-inch  specials,  bends,  tees,  etc.,  in  addition  to 

cost  of  straight  pipe "  .  .  .  .  each 

3-inch  specials,  bends,  tees,  etc.,  in  addition  to 

cost  of  straight  pipe "  .  . .  .      '    

Cast-iron  pipe . "  .  .  .  .  per  Ib. .  . 

Cast-iron  specials,  bends,  etc "  .  . . .     '       ". ... 

Wooden    troughs    for    surface    distribu- 
tion, in  place at  ....  per  loooft.  B.M, 

Filter  Material 

Gravel  filling  around  sub-surface  tile,  placed.,  .at  ....  per  cu.yd. 

Sand  filling  for  artificial  filter  beds "  .  . .  . 

Broken  stone  for  contact  beds  or  for  filters ...."....    " 
Broken  stone  for  sludge  beds "  ....   ' 

Valves 

Gate  valves,  Fig.  13 at  ....  each 

Flap  valves,  Fig.  16 "  .  . .  .      '    

Slide  valves,  Fig.  1 1 "  .  . .  .     "    

Wooden  slide  valves " '    

Sludge  valves,  Fig.  10 "  . . . .     "    


Tools 

Shovels,  long  or  short  handled at each 

Picks "  ....     "    

Wheelbarrows,  wooden  or  steel "  .  . .  .      '    

Sieves  for  screening  sand  and  gravel "  .  .  .  .     "    

Saws,  hammers,  and  axes Total  amount .  . . 


No.  of  i  r  •   . 
Units    Cost 


ESTIMATES   OF   COST 
TABLE  OF  COST.— Continued. 


127 


No.  of 
Units 

Cost 

Lumber 

For  sheeting  and  bracing;   rough  lum- 
ber                              at  ....  per  loooft.  B.M. 

For  forms  for  concrete  work,  sized.  .  .  .  '.  "  .  .  .  .    ' 

For    runways,     staging    and     mixing 
boards  plank                                           "            *' 

Hardware 

Nails  for  forms,  staging,  etc  at  ....  per  100  Ibs. 
Bolts  or  wire  for  concrete  forms  "  .  .  .  .    "    lb  

Iron  Work 
Manhole  frames  and  covers  at  ....  per  lb  

Steps  for  manholes  "  "     "  .  .  .  . 

Siphons 
Flushing  siphons  for  dosing  tank  at  ....  complete. 

Timed  siphons  for  emptying  contact  beds.  .."....        " 

Total  

Cost  of  Maintenance. — As  to  the  cost  of  maintenance,  very 
little  that  is  definite  can  be  said.  Sub-surface  irrigation  plants 
should  require  no  expenditure  except  for  the  occasional  cleaning 
of  the  sedimentation  tank.  If  this  is  emptied  three  times  a 
year,  the  labor  needed  would  amount  to  about  a  half-day's  time 
on  each  occasion  for  a  family  of  ordinary  size.  For  sand  filters, 
either  natural  or  artificial,  the  tank  must  be  emptied  as  with 
sub-surface  irrigation,  and,  in  addition,  the  surface  must  be 
scraped  occasionally,  and  at  the  approach  of  winter  furrows 
must  be  dug.  Perhaps  two  days'  time  would  be  all  that  would 
be  needed  for  a  plant  dealing  with  the  sewage  of  a  single  family. 
A  broken-stone  bed  requires  no  attention  for  seven  or  eight 
years,  and  then  the  stone  has  to  be  shovelled  out,  washed,  and 
replaced. 


128        PRACTICAL   METHODS   OF   SEWAGE   DISPOSAL 

In  none  of  the  installations  is  this  excessive  in  comparison 
with  the  benefits  received,  and  it  should  not  be  considered  a 
burden  to  expend  this  amount  of  time  in  maintaining  so  impor- 
tant a  part  of  the  household  economy  as  the  disposal  of  the 
household  wastes  in  a  sanitary  manner.  It  must  not  be  forgotten, 
however,  that  no  sewage-disposal  plant  is  exempt  from  occasional 
break-down  or  accidents,  and  that  there  must  be  a  constant 
supervision  exercised.  This  supervision  should  not  require  much 
more  time  than  above  suggested,  but  should  be  exercised  for 
the  purpose  of  correcting  irregular  flows  or  distribution  before 
the  value  of  the  plant  is  utterly  destroyed. 


INDEX 

PAGE 

Bacteria,  action  of,  in  reducing  organic  matter  and  sewage 6 

Baffle  boards  in  settling  tank 30 

Broad  irrigation 98 

areas,  maintenance  of 108 

methods  of  applying  sewage  in 104 

sewage  disposal  by,  area  required 102 

when  advisable no 

Clay  soils  for  sewage  purification 9 

Cleaning  settling  tanks .  32 

Composition  of  sewage 4 

Concrete  for  walls  and  floors  of  settling  tanks 24 

walls,  forms  for  constructing 22 

Contact  beds 87 

alternating  flow  to 89 

general  features  of  construction  of 89 

principles  involved 88 

table  for  use  in  constructing 92 

underdrainage  of 89 

Cost  items  of  sewage-disposal  plant,  table  on  which  to  base  estimates.  .  125 

Cost  of  broken  stone 124 

of  concrete 119 

of  dosing  devices  or  siphons 122 

of  excavating  and  refilling 115 

of  finishing  and  cleaning  up 124 

of  forms  for  concrete  walls 121 

of  laying  sewers  and  drains 113 

of  maintaining  sewage-disposal  plants 127 

of  material 113 

for  filter  beds 123 

of  rock  excavation 117 

of  sand 114 

of  sewage-disposal  plants 112 

of  valves 122 

Crops,  yield  of,  with  and  without  sewage  irrigation 103 

Disease,  transmission  of,  by  insects I 

Dosing  apparatus,  Ansonia  automatic 43 

three  kinds  of 53 

Drain  pipe  from  settling  tank 26 

129 


130  INDEX 

PAGE 

Emscher  or  Imhoff  tanks 34 

Excavation  for  settling  tanks 25 

Fertilizing  elements  in  sewage,  value  of 98 

Forms  for  building  settling  tanks 22 

Grease  traps  in  connection  with  sand  filters 78 

Imhoff  or  Emscher  tanks 34 

Irrigation,  amount  of  water  necessary  for 101 

of  orchards 108 

value  of  sewage  for 99 

Laws  against  disposal  of  sewage  into  streams 3 

Manholes  through  settling-tank  roof 29 

Overflow  pipe  from  siphon  chamber 31 

Roof  of  settling  tank,  construction  of 27 

Sand  filters,  alternating  flow  of  effluent  to  different  beds  composing.  .  83 

artificially  constructed 79 

details  of  construction  of 74 

devices  for  dosing 82 

distribution  of  effluent  over 78 

preparation  for  winter  of 84 

quality  of  sand  suitable  for • 86 

scraping  surface  of 84 

settling  of  sewage  before  application  to 77 

table  for  use  in  constructing 76 

underdrainage  of 81 

filtration 74 

Screening  of  sewage : 5 

Settling-tank  floors,  necessary  slope  of 26 

tanks  compared  with  septic  tanks 1 1 

construction  of  floors  of 25 

description  of 16 

dimensions  for 18 

function  of 14 

location  of 20 

near  sub-surface  irrigation  field 31 

materials  for  and  construction  of 20 

operation  of 32 

partial  treatment  only  provided  by 16 

water-tight,  construction  of 24 

Sewage,  composition  and  character  of 4 

disposal — an  engineering  problem I 


INDEX  131 

PAGE 

Sewage  disposal: 

by  dilution 3 

in  soils,  three  essential  conditions  for 8 

need  of 2 

plants,  permissible  rates  of  operation  of 8 

preliminary  and  final  methods  of 1 1 

filters 73 

proper  operation  necessary  to  success  of 96 

relative  efficiency  of  various  types  of 73 

Sewer,  size  and  gradient  of  effluent 63,  77 

Siphon  chamber,  depth  of  sewage  in 38 

chambers 21,60 

necessity  for 37 

Siphon,  Miller 45 

simplest  form  of 44 

Van  Vranken 44 

Siphons,  alternating  air-lock 52 

discharging  depth  or  draught  of 77 

for  automatic  discharge  of  sewage  effluent 42 

how  to  place,  in  position 25,  64,  77 

Merritt 50 

placing  two  in  one  chamber  for  alternating  flow 47 

plural  alternating 48 

sketches  of  and  directions  for  setting  furnished  by  manufacturers  of  53 

Size  of  dose  in  disposal  plants 10 

Sludge  pipe  from  settling  tank 27 

Soils  and  their  suitability  in  purifying  sewage 7 

Sprinkling  filters 93 

construction  and  operation  of 94 

Sub-surface  irrigation,  conditions  favorable  to 71 

description  of 55 

fields,  location  of 58 

soils  suitable  for 57 

special  advantages  of,  for  country  home 57 

system — advantages  over  cesspools 56 

systems,  alternate  use  of  different  portions  of 68 

details  of  construction  of 58,  63 

value  of  underdrainage  in 69 

tables  for  use  in  constructing 59 

underdrains  for 69 

tiling,  depth  below  ground  surface  of 67 

gradient  or  fall  of 67 

how  to  lay 64 

necessary  length  of 66 

Timed  siphons  for  discharging  contact  beds 91 


132  INDEX 

PAGE 

Valves,  English  slide 40 

flap  attached  to  sewer  pipe 41 

with  loose-link  hinges 42 

with  metallic  seat 41 

hand 39 

ordinary  gate 4° 

sluice  gate 40 


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16 


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